Enable scripts to activate/deactivate spawn areas & mapobjects

Renames "isActive" on spawnareas to "isSpawning" - so that a spawn area can be non-spawning but still have monsters left in it.
Adds new scripteffect types:
* "spawnAll" = sets  spawn area to spawning and spawns all monsters
* "removeSpawnArea" = sets a spawn area to non-spawning and removes all mobs
* "deactivateSpawnArea" = sets a spawn area to non-spawning
* "activateMapChangeArea" = sets a mapchange area to non-active
* "deactivateMapChangeArea" = sets a mapchange area to non-active (so that it does not teleport the player)
Adds new property "active" to spawn- and mapchange areas in tmx files, that determines whether the areas are active when starting a new game.
Merge branch 'activate-spawnareas'