add const
use std::bitset instead of vector<bool>

for hotkey scope.
more flexible hotkey scopes

there are some hotkeys that are senseful in editor and in game but not
in teh main menu, so now instead of having hotkeys eigher in GAME,
EDITOR, MAIN_MENU or GENERAL we now allow any combination of the first
3.

this is also intended to fix a bug in add_hotkey() if new_scope ==
hotkey::SCOPE_COUNT where new hotkeys doesn't correctly overwrite other
scoped hotkeys.
Merge pull request #215 from gfgtdf/hotkey_scopes

Hotkey scopes