partially remove resources::game_map (part 1)

This is the result of running, in src/ directory, the following:

find . -type f -exec sed -i 's/resources::game_map->/resources::gameboard->map()./g' '{}' \;

and carefully inspecting the result, and adding "game_board.hpp"
remove resources::game_map (part 2)

This the result of executing, in folder src/, the following

find . -type f -exec sed -i 's/\*resources\:\:game_map/resources\:\:gameboard->map()/g' '{}' \;

and carefully inspecting the result.

We also had to add game_board.hpp includes in various places,
and change the arguent order of unit::is_visible_to_team --
this function was taking *resources::game_map as its default
argument, and we do not want to include game_board in unit.hpp,
as it creates cyclic dependencies. This was resolved by
eliminating this as a default value -- this is an improvement,
since usually when this function was called it was in a context
where a game_map was available already locally anyways.
finish removing resources::game_map

The remaining uses are just, checking whether or not the pointer
is null, or resets to its value, or simply storing it in a local
variable.

It might be appropriate to add resources::game_map back as a
function taking no parameters, at least this is flexible
enough to be changed later easily.
Merge branch 'master' of git://github.com/wesnoth/wesnoth