"conveniency" update

Player constructor now requires the second canvas as a parameter.
Player methods now don’t require a canvas to work
CatanGame was modified to work with changes
CatanGame has method to toggle its buttons
OpenTrade - names of trading players are centered properly now
OpenTrade constructor requires CatanGame as parameter
OpenTrade disables main window’s buttons, so that users cannot do
anything except trading while trading is open.