create a board model class to store tile models
WECommand class for holding game actions
WEStack class for holding WECommands
create methods for WEStack and store an instance in player moves
update replay available method to accommodate WEStack configuration
WEStack only adds commands if not playing back moves
method for adding commands to stack
rename WEFallingTiles
swap instances are created with tile types for every swap type made
player moves combines the move with a current board model and passes to the stack