Tweak the Averguard Temple door

- The door now displays a message if the player has neither the key nor
the talisman.
- Once the door has been opened, it will stay open. Even after leaving
the map.
Merge pull request #434 from dorkster/alpha_demo

Tweak the Averguard Temple door
Remove some obsolete keys from various data files

Note: maps still complain about 'tilewidth' and 'tileheight'. These are
indeed obsolete, but we should patch the Flare plugin for Tiled before
removing them here. Otherwise, we'll probably add them again by
accident.
Merge pull request #435 from dorkster/cleanup

Remove some obsolete keys from various data files
Remove unused key from npcs/
Merge pull request #436 from mazayus/fixes

Remove unused key from npcs/