Region-Tiling, Bug Fixes, Relative Pathing

Added in support for region-based tile-placement (destview.h,
destview.cpp, mapview.h, mapview.cpp)

Fixed a segmentation fault where the global toolkit tile selection would
emit a cleared() signal in its deconstructor (tileselection.cpp)

Fixed a memory leak when Areas are deleted (area.cpp)

Focus is now given back to the Map View when a selection is made
(sheetview.h, sheetview.cpp, sheetwidget.cpp, mapview.cpp)

The new area dialog now retrieves relatives paths from the 'Browse...'
button (newareadialog.cpp)