Add CLI entrypoint

[gsheni]

• Add entrypoint to add/override cli commands. Featuretools will look at the entrypoints under featuretools_cli, and assuming a dictionary called commands, it will add/override those CLI commands.
  -commands should be a dict with {'name': 'command'). The command should be a function with the @click decorator.
• running featuretools info in the CLI prints our more information.

[codecov]

Codecov Report

Merging #493 into master will decrease coverage by 0.23%.
The diff coverage is 53.84%.

@@            Coverage Diff            @@
##           master    #493      +/-   ##
=========================================
- Coverage   96.34%   96.1%   -0.24%     
=========================================
  Files         106     108       +2     
  Lines        8802    8853      +51     
=========================================
+ Hits         8480    8508      +28     
- Misses        322     345      +23

Impacted Files	Coverage Δ
featuretools/__main__.py	0% <0%> (ø)	⬆️
featuretools/tests/utils_tests/test_cli_utils.py	100% <100%> (ø)
featuretools/utils/api.py	100% <100%> (ø)	⬆️
featuretools/utils/cli_utils.py	89.47% <89.47%> (ø)

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[kmax12]

LGTM