BuildingEd: Added "shallow" roof caps and slopes.
Don't fail if virtualtilesets.vts doesn't exist.
BuildingEd: Cleaned up the roof-corner-tile code.
Replaced duplicate code in BuildingMap with an inline method.
BuildingEd updates the floor above when manipulating objects.

Some objects (such as stairs and roof objects) may affect tiles on the floor
the one the object is on.
BuildingEd: Fixed hand cursor not displaying after mousing-over a roof's resize-handle.

QGraphicsView sets the cursor (when the mouse is over an item) on the
viewport widget, not on itself.  It seems there is a bug though, because
QWindow::unsetCursor() is never called after leaving an item if the viewport
never had a cursor set on it; QWindow::setCursor() is called with whatever
cursor was set on the viewport widget before mousing over the item.