Tile highlighting, zoom hotkeys, reset view, directory bug fix, Change
Area bug fix

Tile highlighting (with a selection, while selecting, or while placing)
renders solid lines around the edges of the current selection (top,
bottom, left, right), determined by a "TileSpecialDecoration" See:
tileitem.h, tileitem.cpp, sourceview.cpp

Ctrl+Minus and Ctrl+Plus are added as hotkeys for zooming out and in
respectively in Map View. Sheet View cannot have focus, so they will not
work (Ctrl+Scroll still works). See: sheetview.cpp, mapview.cpp

Space resets the view(s) to their default transformation at the top left
(since previous commit; support added for Sheet View in this commit,
although the same problem as above persists). See: sheetview.cpp,
mapview.cpp

Fix a bug where "Open" uses the last-accessed directory instead of the
default <Application>/../ directory in Ubuntu. See: toolkitwindow.cpp

Fix a bug where changing areas renders a garbage selection. See:
destview.cpp