== operator not defined for multioutput columns features

### == operator not defined for multioutput columns features

```py
import featuretools as ft
from featuretools.tests.testing_utils import make_ecommerce_entityset

es = make_ecommerce_entityset()

feature_defs = ft.dfs(entityset=es,
target_entity="customers",
agg_primitives=["n_most_common"],
trans_primitives=[],
features_only=True)

f = feature_defs[6]
f == f
```
```py
AssertionError Traceback (most recent call last)
in
----> 1 f == f

~/workspace/featuretools/featuretools/feature_base/feature_base.py in __eq__(self, other)
221 def __eq__(self, other):
222 """Compares to other by equality"""
--> 223 return self._handle_binary_comparision(other, primitives.Equal, primitives.EqualScalar)
224
225 def __ne__(self, other):

~/workspace/featuretools/featuretools/feature_base/feature_base.py in _handle_binary_comparision(self, other, Primitive, PrimitiveScalar)
215 def _handle_binary_comparision(self, other, Primitive, PrimitiveScalar):
216 if isinstance(other, FeatureBase):
--> 217 return Feature([self, other], primitive=Primitive)
218
219 return Feature([self], primitive=PrimitiveScalar(other))

~/workspace/featuretools/featuretools/feature_base/feature_base.py in __new__(self, base, entity, groupby, parent_entity, primitive, use_previous, where)
736 primitive=primitive,
737 groupby=groupby)
--> 738 return TransformFeature(base, primitive=primitive)
739
740 raise Exception("Unrecognized feature initialization")

~/workspace/featuretools/featuretools/feature_base/feature_base.py in __init__(self, base_features, primitive, name)
634
635 # R TODO handle stacking on sub-features
--> 636 assert all(bf.number_output_features == 1 for bf in base_features)
637
638 super(TransformFeature, self).__init__(entity=base_features[0].entity,

AssertionError:
```
-----

#### Bug/Feature Request Description

The == operator correctly checks for equality in single column output features. For features with multiple output columns, the operator throws an AssertionError.

Temporary workaround is to use `feature.unique_name()` to compare two features directly.

#### Expected Output

``

#### Output of ``featuretools.show_info()``

Featuretools version: 0.9.1
Featuretools installation directory: /Users/alex/workspace/featuretools/featuretools

SYSTEM INFO
-----------
python: 3.7.3.final.0
python-bits: 64
OS: Darwin
OS-release: 18.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

INSTALLED VERSIONS
------------------
numpy: 1.16.2
pandas: 0.24.2
tqdm: 4.31.1
toolz: 0.9.0
PyYAML: 5.1
cloudpickle: 0.8.0
future: 0.17.1
dask: 2.0.0
distributed: 1.26.0
psutil: 5.6.1
Click: 7.0
scikit-learn: 0.20.3
pip: 19.0.3
setuptools: 40.8.0