Fix potential issues displaying keys in HUD

Use (B/R/Y)KEYA0 and (B/R/Y)SKUA0 instead of (B/R/Y)KEYB0 and
(B/R/Y)SKUB0 in HUD. Also, when determining what keys are needed in a
level, look at all the doors in the level as well as all the keys. This
fixes issue with Batman TC: since blue keys aren't spawned in a level,
and instead dropped by enemies, this causes wrong sprite to flash in HUD
when trying to open a locked blue door. This also fixes no blue key
given when using the IDKFA cheat.