Changes for tackling the LevelOfTheory errors

[rdguha1995]

This PR is mainly to address https://github.com/materialsproject/emmet/issues/933 . A validate_lot flag has been added to the TaskDoc.from_directory function. It defaults to True and performs a check on the given functional and basis set with the MP compatible functionals and basis sets. But if it is turned to False, users can then supply their own functionals and basis sets

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 91.30435% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 90.02%. Comparing base (d334889) to head (83ea3fb).

Files	Patch %	Lines
emmet-core/emmet/core/qchem/calculation.py	89.47%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #970   +/-   ##
=======================================
  Coverage   90.01%   90.02%           
=======================================
  Files         138      138           
  Lines       13164    13175   +11     
=======================================
+ Hits        11850    11861   +11     
  Misses       1314     1314           

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