Updated task-list and minor code cleanup
On winning, game grid now goes slightly opaque while the user is prompted for action; removed 'won' tile
Losing the game now grays out the grid and pops up a modal dialog; the 'lost' tile was removed; task-list updated
Encapsulated some code from MainWindow constructor (layout_score_box)
Removed the reset button
Updated task-list
Added a menu bar and a Game menu and activated the Game | Quit option; other options still have blank handlers