Added keyboard shortcuts to switch BuildingEd modes.

The function keys F1-F4 switch between modes.
Fixed and organized BuildingEd QSettings stuff.
Fixed remembering/restoring the current tool when switching modes in BuildingEd.
Renamed "Clean-up" to "Remove unused entries" in BuildingEd category dock.
Added View > Views menu to hide/show BuildingEd toolbars and docks.
Fixed CategoryDock::resetUsedTiles() removing used building wall grime tile.
Changed BuildingEd's "Floor 1/N" label to a button that displays the Floors Dialog.
Fixed compilation under g++.

It is incredible MSVC choked down some of this code.
Added status text to BuildingEd's PickTileTool.
Don't allow CategoryDock's splitter to collapse child widgets.
Fixed BuildingEditorWindow not updating actions when 'Show Objects' changed.