Debugger: Another set of #13800 fixes.

AbstractTable/Table/TreeTable:
- Let BColumnListView take care of deleting columns. The previous
approach was resulting in the columns being leaked.

Debugger:
- Don't detach the UI reference, as TeamDebugger will acquire its own.

GraphicalUserInterface:
- Cleanup of file panel handler.

SourceView:
- Clean up marker manager.

*Roster:
- Clean up registered objects in destructors.

GlobalTypeLookup:
- Clean up hash tables.

NetworkTargetHostInterfaceInfo:
- Fix reference handling for settings.

Debugger: Relocate value_handlers.

- As they are currently only used by the VariablesView, move ValueHandler
and related code into user_interface/gui.