Add variable types plotting, and variable page to docs

[gsheni]

Pull Request Description

• Fixes Create UML-Diagram in Docs for Variable Types #990
• Created list_variable_types function (similar to list_primitives)
• Separates out the EntitySet plotting into separate utils file to be used by other functions
• Moves find_variable_types into utils of variables

[codecov]

Codecov Report

Merging #1013 into master will increase coverage by 0.02%.
The diff coverage is 98.03%.

@@            Coverage Diff             @@
##           master    #1013      +/-   ##
==========================================
+ Coverage   98.26%   98.29%   +0.02%     
==========================================
  Files         121      124       +3     
  Lines       12467    12541      +74     
==========================================
+ Hits        12251    12327      +76     
+ Misses        216      214       -2     

Impacted Files	Coverage Δ
featuretools/utils/plot_utils.py	92.00% <92.00%> (ø)
featuretools/entityset/deserialize.py	100.00% <100.00%> (ø)
featuretools/entityset/entity.py	96.16% <100.00%> (ø)
featuretools/entityset/entityset.py	97.63% <100.00%> (+0.40%)	⬆️
featuretools/tests/entityset_tests/test_entity.py	100.00% <100.00%> (ø)
...etools/tests/entityset_tests/test_serialization.py	99.63% <100.00%> (ø)
...aturetools/tests/variables/test_variables_utils.py	100.00% <100.00%> (ø)
featuretools/variable_types/api.py	100.00% <100.00%> (ø)
featuretools/variable_types/utils.py	100.00% <100.00%> (ø)
featuretools/variable_types/variable.py	98.70% <100.00%> (-0.02%)	⬇️
... and 4 more

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[gsheni]

Page on Docs:
https://docs.featuretools.com/en/add_variable_page/variables.html

[thehomebrewnerd]

You might also want to review the documentation in using_dask_entitysets.rst and update the information in the Entity Limitations sections to use list_variable_types() instead of the current suggestion to use featuretools.variable_types.find_variable_types().

[gsheni]

You might also want to review the documentation in using_dask_entitysets.rst and update the information in the Entity Limitations sections to use list_variable_types() instead of the current suggestion to use featuretools.variable_types.find_variable_types().

@thehomebrewnerd Fixed this.

[thehomebrewnerd]

Looks good!

[rwedge]

Looks good