Add support for table indent

[Trainmaster]

Description

This adds support for table indent (http://www.datypic.com/sc/ooxml/e-w_tblInd-1.html)

Checklist:

• I have run composer run-script check --timeout=0 and no errors were reported
• The new code is covered by unit tests (check build/coverage for coverage report)
• I have update the documentation to describe the changes

[Trainmaster]

@troosan I'd suggest to remove the unit in the table style options and also use \PhpOffice\PhpWord\ComplexType\TblWidth for the width option. Imho it makes no sense to use the same unit for both table style options.

[troosan]

Indeed, I agree, it makes sense to use the TblWidth everywhere.
If you do the change, make sure you keep the getters/setters to keep backward compatibility.
Just mark them as deprecated so we do not forget to remove them in version 1.0

[Trainmaster]

@troosan Alright. But I'll do that in a separate pull request.