resources::game_map is const *, move functionality to game_board

This commit changes the resources::game_map pointer to a const *,
so that changes to the game_map coming from lua or wml apis must
go through the game_board. Three functions were moved into the
game_board -- although substantively they did not change, there
were minor changes, in terms of the kind of error reporting done,
and also in how gui refresh orders are issued afterwards. In
testing the differences due to this refactor don't seem to be
noticeable.
Merge branch 'restrict_game_map'