Heavily awesomified smashing, other misceries.

- Added latest barrel assets and deleted old.
- Created barrel debris assets, which also have little trail effects :D.
- Put smoke back in, tweaked colour and particle size
- Assetified many things in prefab asset folder
- SMASHING THINGS looks more awesome: debris are created at random
points on an object's surface and are blasted away from the destroyed
object's centre by a slightly randomised explosion value.  Debris have
little trails which could use tweaking I guess but really add to it imo.

- Replaced the wall tiles and made it 3 tiles across.  Not sure of
optimal tile size/street width...