Add support for destructable map tiles

[lendrick]

Tiles that disappear when you shoot them are good for adding secrets. When we start adding in specific weapons, it would be nice to have tiles that respond only to certain damage types (fire, grenades, etc).

Since you can't (to my knowledge) give attributes to individual tiles in tiled, the way I'm thinking this might be accomplished is by drawing objects on tiled that specify certain tile attributes (how much damage a tile requires to destroy it, what type of damage, etc) and then having the map loader check those objects and set attributes for all the tiles under them.

[lendrick]

The other possibility is (if we go the physics route) to just make actors that look like map tiles.