0.8.3a1 - Clear on change Area, save all

Changing the active Area clears the selection and does not redraw the
entire map in MapView.

Save As is replaced by Save All with the shortcut Ctrl+Shift+S

if/else blocks in SheetView and MapView are replaced by switch
statements to improve readability.

MapView calls selectionMoveEvent() instead of manually clearing and
resetting the selection (redundant code...)

Comments have been added to sourceview.h and destview.h. See the headers
for implementation details and derived-class tips.