Fusion Graph: wheelEvent causes error

##### Data Fusion version

0.1.11

##### Orange version

3.24.dev

##### Expected behavior
Fusion Graph works.

##### Actual behavior
Fusion Graph crashes when using mouse scroll in the view.

##### Steps to reproduce the behavior
In Fusion Graph, one the view is set, use mouse scroll.

##### Additional info (worksheets, data, screenshots, ...)

```
Exception: | AttributeError: 'QWheelEvent' object has no attribute 'orientation'
-- | --
Module: | orangecontrib.datafusion.widgets.graphview:429
Version: | 3.24.0.dev
Environment: | Python 3.7.2 on Darwin 17.7.0 Darwin Kernel Version 17.7.0: Fri Oct 4 23:08:59 PDT 2019; root:xnu-4570.71.57~1/RELEASE_X86_64 x86_64
Installed Packages: | AnyQt==0.0.10, Babel==2.6.0, Bottleneck==1.2.1, CacheControl==0.12.5, CherryPy==18.1.1, Click==7.0, Cython==0.29.12, Fiona==1.8.9.post2, GDAL==2.3.3, Genesis-PyAPI==1.2.1, Jinja2==2.10, Keras-Applications==1.0.8, Keras-Preprocessing==1.1.0, Keras==2.3.1, Lemmagen==1.2.0, Mako==1.1.0, Markdown==3.1.1, MarkupSafe==1.1.0, Orange-Spectroscopy==0.4.7, Orange3-Associate==1.1.5, Orange3-Bioinformatics==4.0.1.dev9+g267c7dd, Orange3-DataFusion==0.1.11, Orange3-Educational==0.2.1, Orange3-Geo==0.2.5, Orange3-ImageAnalytics==0.4.1, Orange3-Lookalike-Demo==0.1.0, Orange3-Network==1.5.0, Orange3-Prototypes==0.12.0, Orange3-SingleCell==0.9.1.dev138+g0a3a944, Orange3-Text==0.8.0.dev0+e1d92ef, Orange3-Timeseries==0.3.3, Orange3==3.24.0.dev0+bf1dc93, Pattern==3.6, Pillow==6.2.1, PyPDF2==1.26.0, PyQt5-sip==4.19.19, PyQt5==5.13.1, PyQtWebEngine==5.13.1, PySocks==1.6.8, PyYAML==5.1, Pygments==2.3.1, Rtree==0.8.3, Send2Trash==1.5.0, Shapely==1.6.4.post2, Sphinx==2.0.1, Theano==1.0.4, Unidecode==1.0.23, Werkzeug==0.16.0, Wikipedia-API==0.5.3, XlsxWriter==1.1.2, absl-py==0.8.1, alabaster==0.7.12, altair==2.4.1, anndata==0.6.22.post1, appnope==0.1.0, asn1crypto==0.24.0, astor==0.7.1, astroid==2.2.5, atomicwrites==1.3.0, attrs==18.2.0, backcall==0.1.0, backports.csv==1.0.7, backports.functools-lru-cache==1.5, beautifulsoup4==4.7.1, biopython==1.73, bleach==3.1.0, blis==0.2.4, bokeh==1.0.4, boto3==1.9.88, boto==2.49.0, botocore==1.12.88, branca==0.3.1, brotlipy==0.7.0, bz2file==0.98, certifi==2019.9.11, cffi==1.12.2, chardet==3.0.4, cheroot==6.5.4, click-plugins==1.1.1, cligj==0.5.0, colorcet==0.9.1, commonmark==0.8.1, cryptography==2.5, cycler==0.10.0, cymem==2.0.2, decorator==4.3.2, defusedxml==0.5.0, distro==1.4.0, doc8==0.8.0, docutils==0.14, docx2txt==0.7, dropbox==9.3.0, elmoformanylangs==0.0.2, en-core-web-sm==2.1.0, entrypoints==0.3, extranormal3==0.0.3, fastdtw==0.3.2, feedparser==5.2.1, folium==0.8.0, funcy==1.11, future==0.17.1, gast==0.3.2, gensim==3.7.1, geopandas==0.6.1, google-compute-engine==2.8.13, grpcio==1.23.0, h2==2.6.2, h5py==2.9.0, holidays==0.9.10, hpack==3.0.0, hyperframe==3.2.0, hypertemp==0.8.0, idna==2.8, imagesize==1.1.0, importlib-metadata==0.23, ipykernel==5.1.0, ipython-genutils==0.2.0, ipython==7.2.0, ipywidgets==7.4.2, isort==4.3.17, jaraco.functools==2.0, jedi==0.13.2, jmespath==0.9.3, joblib==0.13.1, json-spec==0.10.1, jsonschema==3.0.0a3, jupyter-client==5.2.4, jupyter-console==6.0.0, jupyter-core==4.4.0, jupyter==1.0.0, keyring==17.1.1, keyrings.alt==3.1.1, kiwisolver==1.0.1, langdetect==1.0.7, language-check==1.1, lazy-object-proxy==1.3.1, llvmlite==0.27.1, lockfile==0.12.2, loompy==2.0.17, lxml==4.3.1, matplotlib==3.0.3, mccabe==0.6.1, mistune==0.8.4, mkl-fft==1.0.13, mkl-random==1.0.4, more-itertools==5.0.0, msgpack==0.6.1, munch==2.4.0, murmurhash==1.0.0, mysqlclient==1.4.2.post1, natsort==6.0.0, nbconvert==5.3.1, nbformat==4.4.0, ndf==0.1.4, networkx==2.2, nltk==3.4, notebook==5.7.4, numba==0.42.1, numexpr==2.6.9, numpy==1.16.4, oauthlib==3.0.1, odfpy==1.4.0, olefile==0.46, openTSNE==0.3.11, opencv-python==4.0.0.21, orange-canvas-core==0.1.9.dev0, orange-widget-base==4.2.0.dev0+abbb4ad, overrides==1.9, packaging==19.0, pandas-datareader==0.7.0, pandas==0.24.1, pandocfilters==1.4.2, parso==0.3.2, patsy==0.5.1, pbr==5.2.1, pdfminer3k==1.3.1, pexpect==4.6.0, pickleshare==0.7.5, pip==19.0.1, pkginfo==1.5.0.1, plac==0.9.6, plotly==3.6.0, pluggy==0.8.1, ply==3.11, point-annotator==1.0.0, polyglot==16.7.4, portend==2.4, preshed==2.0.1, prometheus-client==0.5.0, prompt-toolkit==2.0.8, protobuf==3.9.2, ptyprocess==0.6.0, py==1.7.0, pyLDAvis==2.1.2, pyOpenSSL==19.0.0, pyclipper==1.1.0.post1, pycparser==2.19, pycryptodome==3.8.1, pyemd==0.5.1, pygpu==0.7.6, pylint==2.3.1, pynndescent==0.3.3, pyparsing==2.3.1, pyproj==1.9.6, pyqtgraph==0.10.0, pyrsistent==0.14.9, pyspellchecker==0.5.1, pytest==4.2.0, python-dateutil==2.8.0, python-docx==0.8.10, python-louvain==0.13, pytz==2018.9, pyzmq==17.1.2, qtconsole==4.4.3, readme-renderer==24.0, recommonmark==0.5.0, requests-cache==0.5.2, requests-oauthlib==1.2.0, requests-toolbelt==0.9.1, requests==2.22.0, restructuredtext-lint==1.3.0, retrying==1.3.3, rfc3986==1.2.0, s3transfer==0.1.13, scikit-fusion==0.2.1, scikit-learn==0.20.2, scipy==1.3.0, seaborn==0.9.0, serverfiles==0.3.0, setuptools-git==1.2, setuptools==42.0.1, simhash==1.9.0, simplejson==3.16.0, singledispatch==3.4.0.3, sip==4.19.8, six==1.12.0, sklearn==0.0, slumber==0.7.1, smart-open==1.8.0, snowballstemmer==1.2.1, sortedcontainers==2.1.0, soupsieve==1.7.3, spacy==2.1.4, spectral==0.19, sphinxcontrib-applehelp==1.0.1, sphinxcontrib-devhelp==1.0.1, sphinxcontrib-htmlhelp==1.0.2, sphinxcontrib-jsmath==1.0.1, sphinxcontrib-qthelp==1.0.2, sphinxcontrib-serializinghtml==1.1.1, srsly==0.0.5, statsmodels==0.10.0, stevedore==1.30.1, tempora==1.14, tensorboard==1.13.1, tensorflow-estimator==1.13.0, tensorflow==1.13.1, termcolor==1.1.0, terminado==0.8.1, testpath==0.4.2, thinc==7.0.4, toolz==0.9.0, torch==1.1.0, tornado==5.1.1, tqdm==4.32.1, traitlets==4.3.2, tweepy==3.7.0, twine==3.1.1, ufal.udpipe-temp==1.2.0.5, ufal.udpipe==1.2.0.3, urllib3==1.24.1, validate-email==1.3, vincent==0.4.4, virtualenv==16.7.7, wasabi==0.2.2, wcwidth==0.1.7, webencodings==0.5.1, wheel==0.33.6, widgetsnbextension==3.4.2, wikipedia==1.4.0, wmd==1.3.1, wrapt==1.11.1, xlrd==1.2.0, zc.lockfile==1.4, zipp==0.6.0
Machine ID: | ajda
Stack Trace: | Traceback (most recent call last):  File "/Users/ajda/orange/orange3-datafusion/orangecontrib/datafusion/widgets/graphview.py", line 429, in wheelEvent    if event.orientation() != Qt.Vertical: returnAttributeError: 'QWheelEvent' object has no attribute 'orientation'
Local Variables: | OrderedDict([('event', ),             ('self',              )])
```

Start in orangecontrib/datafusion/widgets/graphview.py at line 429 and reproduce the crash by opening Fusion Graph and scrolling. Inspect the QWheelEvent usage involved in wheelEvent. Done means mouse scrolling no longer raises the reported AttributeError and Fusion Graph continues working.

Written by the indexing model from the issue text.