Hack together Map class. Doesn't work yet.
Get game working with new Map class.
Fix explosions.
Tidy up Cell creation.
Rename some images.
Create new file for Bear.

Several bear-related functions still in main.py.
Actually move images, remove old 'bear.py'
Hack ALL the files!
Remove more message stuff, make player transparent.
Pull out (and break) the HUD.
Start moving stuff to World.
Get bears moving in World.
Move exploding to Player.
Fix and re-enable the HUD.
Restore endgame messages.
Stop bears being inescapable.
Move scrolling code out of main.py.
Tidy main.py slightly.
More fiddling.
Fix visible bears, delayed quitting.