Substack should not be allowed to change columns

Substack should not be allowed to change columns

Disable the arguments append-column and delete-column of tabular-features.

The code is taken from InsetMathCases, with some changes
* no need to record undo here
* in dispatch, return is prefered to break, since we do not want to invoke
  InsetMathGrid::doDispatch.
Propagate these changes to InsetMathCases.

Cleanup of the InsetMathCases error messages to fit with other parts
of the code.

The handling of tabular-features in mathed needs to be unified somehow.

Based on a commit from lynx <lorenzobertini97@gmail.com>

Part of bug #12590.