Fix instantiated LogicalType bugs

[tamargrey]

closes #230

• Adds a utils function to just get the LogicalType class for any logical type whether it's instantiated or not
• Fixes problem with checking if Datetime() is a class
  • fixes subclass issue in describe
  • fixes subclass issue in mutual info
  • fixes subclass issue in select (ignored select_ltypes and semantic tags bc they're bing removed)

[codecov]

Codecov Report

Merging #231 into main will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #231   +/-   ##
=======================================
  Coverage   99.95%   99.95%           
=======================================
  Files          22       22           
  Lines        2270     2301   +31     
=======================================
+ Hits         2269     2300   +31     
  Misses          1        1           

Impacted Files	Coverage Δ
woodwork/data_column.py	100.00% <100.00%> (ø)
woodwork/data_table.py	100.00% <100.00%> (ø)
woodwork/tests/data_table/test_datatable.py	100.00% <100.00%> (ø)
woodwork/utils.py	100.00% <100.00%> (ø)

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[gsheni]

looks good!