Converts Minesweeper's main widget to GML, polishes the custom
game window, formats the clock as human readable digital time, and
defers invoking Field's callback until the main widget has finished
relayout. Fixes inability to downsize the main window when shrinking
field size.
This change makes it easier to generate a new field. Instead of using
hard-coded values everywhere, we now just need to keep track of
the Difficulty enum value.
This adds a dialog window which allows us to customize the size of the
board and the amount of mines that will be placed.
The current max amount of mines is 50% of the total number of cells
due to the fact that the generator algorithm takes too long to create a
board for higher percentages of mines.