Speed up periodical map unloading by moving beginSave() and endSave() to outer loop in Map::timerUpdate()

Fix some texture stuff: remove item_fence.png, use fence.png, remove inexisting cactus.png from texture atlas (replace with nothing because cactus is rare)

Also, the temp item wasn't being deleted, might have been a memory leak.
Now you will only eat 1 item off a stack

* The map will reside in world/map.sqlite
* It will load from the sectors folder but will not save there

* I didn't understand that expression last fix and now the furnace would burn fuel
even when it had no source item.