Click-n-drag to select multiple tiles

	The main purpose here is to facilitate testing of
	the functions tile_group_is_set and tile_group_is_run.
	Eventually it will be improved for general UI purposes.
	Grouped tiles are printed to terminal.

	XXX There is a bug here XXX
	Selections must:
	(a)start above the highest tile and catch all the
	top left corners of each tile
	OR
	(b)start below the lowest tile and catch all the
	bottom left corners of each tile