Updated RandomWalkAI, PlayableCharacter, and World classes

RandomWalkAI now has a bounding box so the NPCs don't go all over the
place. PlayableCharacter now only checks collision if the player is
moving. World now creates two NPCs and sets their spawn points (as well
as the player's) and walking boundaries based on the .tmx map file.
Merged with stuff from last few min

Merged, read other merge commit for more details