Dispose a bunch of Cairo surfaces
[Ide] Destroy workbench on shutdown

Instead of depending on finalizers to do the cleanup.
[Ide] Fix DockNotebook container implementation
Added PlatformService.IsModalDialogRunning()

Mac platform can now provide a more reliable implementation
that takes native dialogs into account.
[Ide] Only show framework options for DotNetAssemblyProject

This enables other DotNetProject subclasses to show custom framework
selector widgets.
[Ide] Fix Mac search keybinding in Edit References
[Ide] Fix another bad container forall