Type checking ignore entities.

[WillKoehrsen]

Addresses #192 by checking the type of ignore_entities (using isinstance) when running dfs. Passing in any type other than a list will result in a TypeError.

This is an update because the authorship on two of the commits for the previous pull request were incorrect.

[codecov-io]

Codecov Report

Merging #193 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #193      +/-   ##
==========================================
- Coverage    93.2%   93.19%   -0.01%     
==========================================
  Files          70       70              
  Lines        7715     7719       +4     
==========================================
+ Hits         7191     7194       +3     
- Misses        524      525       +1

Impacted Files	Coverage Δ
...ols/tests/dfs_tests/test_deep_feature_synthesis.py	98.33% <100%> (+0.01%)	⬆️
featuretools/synthesis/deep_feature_synthesis.py	92.61% <100%> (+0.04%)	⬆️
featuretools/utils/gen_utils.py	64.44% <0%> (-2.23%)	⬇️

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[kmax12]

Looks good, merging.