TableEditor could propose a restricted mode that allows entry insertion from a dropbox

**Vincent HERILIER** ([Bug 60233](https://bz.apache.org/bugzilla//show_bug.cgi?id=60233&redirect=false)):
It could be useful to allow TableEditor to propose a list of entries (within a dropbox) to be inserted at the first column of its table.
Using the TAG property like for Dropbox testbean to populate a list of choices, it could switch the TableEditor to a restricted mode that disables the bottom "Add" button and enables a top dropbpox with a new "Add" button that inserts the selected value.

Maybe a separate widget may be more appropriate.

I can provide one or other solution in a future PR.

Thank you for your feedbacks

Vincent

OS: All