Debugger: Minor fix to text control editor.

TableCellTextControlEditor:
- Switch BTextControl inheritance to public, as gcc2 otherwise fails to
properly dynamic_cast to BTextControl, which breaks the latter
internally.

Debugger: Add interface subclasses for table cell editors.

TableCellTextControlEditor:
- Serves as a base for editors that expose their functionality via a
text control. Handles common functionality of watching for changes,
validating input, and notifying listeners appropriately.
TableCellOptionPopUpEditor:
- Serves as a base class for editors where the set of possible values
is fixed and known up front. Handles reacting to selection changes
and notifying listeners.

Debugger: Minor fix to text control editor.

TableCellTextControlEditor:
- Switch BTextControl inheritance to public, as gcc2 otherwise fails to
properly dynamic_cast to BTextControl, which breaks the latter
internally.

Debugger: Add interface subclasses for table cell editors.

TableCellTextControlEditor:
- Serves as a base for editors that expose their functionality via a
text control. Handles common functionality of watching for changes,
validating input, and notifying listeners appropriately.
TableCellOptionPopUpEditor:
- Serves as a base class for editors where the set of possible values
is fixed and known up front. Handles reacting to selection changes
and notifying listeners.