Disallowed closing Output/Console/Project tabs (fixes #310).
Updated stack/watch panel captions to be invisible (ref #305).
Switched to AuiToolBar as it provides buttons with dropdowns (ref #305).
Updated application icons (ref #305).
Added `Choose Project Directory` to the toolbar (ref #305).
Added toolbar button dropdown with recent projects (ref #305).
Switched to plain background for the toolbar (ref #305).
Removed the gripper on the toolbar (ref #305).