Create TableWorkspaceValidator

[ktactac-ornl]

Description of work

Creates TableWorkspaceValidator and TableWorkspaceNotEmptyValidator as an example.

Summary of work

TableWorkspaceValidator class is created and exposed to the python api
TableWorkspaceNotEmptyValidator inherits and validates that a TableWorkspace is not empty, and is exposed to the python api.
Future derived classes can follow suite.
WorkspaceValidators.cpp is created to expose the classes.

Implementation is analogous to the already existingMatrixWorkspaceValidator

To extend the ability of validation to TableWorkspaces.

Fixes #xxxx.

6817: Expose WorkspaceValidators to Python

Further detail of work

To test:

Follow the mantid documentation for python unit testing

PYTHONPATH=/path/to/build/bin python3 /path/to/src/Framework/PythonInterface/test/python/mantid/dataobjects/WorkspaceValidators.py

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[dlcaballero16]

Code looks good and tests run and pass as expected.