Framework build on macOS

Currently conda-forge iPython does not launch with the framework build of Python, which means it can't be used for interacting with wxPython applications (for example setting matplotlib backend to wx). If I understand [this](https://conda.io/docs/building/meta-yaml.html#python-app) correctly, it might be possible to fix this with as little as adding:

```
build:
osx_is_app: True
```

and probably adding the python.app dependency.

Test:

```
In [1]: import matplotlib as mpl

In [2]: mpl.use('wx')

In [3]: from matplotlib import pyplot as plt

In [4]: plt.plot([0, 1])
An exception has occurred, use %tb to see the full traceback.

SystemExit: This program needs access to the screen.
Please run with a Framework build of python, and only when you are
logged in on the main display of your Mac.
```