Add Battle Mechanism

[hentai-chan]

This is probably going to be the second to last issue:

• implement the remaining functions that are necessary to play the game (make_move, etc.)
• print move table
• catch invalid user input
• ensure that configure_move_set generates at least one move of type MoveType::ATTACK
• balance difficulty
• add the main event loop in main.cpp; add this point the game should be about done

Once this PR is merged test the game thoroughly and return helpful error messages in case something goes wrong.

[hentai-chan]

Note: As for the fourth point in this list, be aware that this fails if the source (this->all_moves) doesn't contain any moves where move.power>0. While this is generally true for all pokemons, there are a few exceptions to this rule, for example ditto (id=132).