Initial steps for a TableNode editor.
Add a table example.
Activate table editor plugin.
Implemented a custom context for Table editing.
Initial version of a TableInspector widget.
TableInspector: row deletion and insertion.
First implementation of Table column insertion and deletion.
Table: create and delete.
Introduce a dedicated action for creating a table.
Improve table styling.
Do not create a table via TableInspector.
Set a proper selection after inserting a new table column.
Do not allow that TableCells are merged by delete/backspace.
Set selection after inserting a row.
Minimal width for empty table cells.
Refactored TableInspector to be replaced by a simple Widget instead.

Using an Inspector for Tables turned out to make things more complicated
than simpler. This refactor streamlined the whole implementation by using
simple widgets instead.
Experimental display of rulers to improve feedback about table manipulations.
Minor tweak of images for table row/col deletion.
Provide some visual feedback for table manipulations.
Hide the table widget after deleting the table.