Add the possibility to find items in containers in the world about andors-trail HOT 4 CLOSED

Should this containers refill or are they empty after the first time?

That depends on the item. A chest with an emerald would not refill but a 
beehive with honey would. Unless you kill all bees, that is.

Containers are now implemented in the code. They use the same logic as usual 
loot bags, but are just not shown as lootbags on the mainview. Mapobject type 
"container" can now be created, that will use a droplist to determine what 
items should be in the container initially.

Since we are re-using the loot bag logic, they will be persisted in the 
savegame file. Anything you place in the container will be persisted, and any 
contents (partial or full) will also be persisted.

Containers will be stocked with new items the first time you enter the map (or 
load a savegame older than 0.6.8).

When creating maps, we should place graphic objects (chests, item piles) to 
make it obvious that there is something that can be picked up on such tiles.

Now we just need to update the maps to place container mapobjects on the maps 
that should contain them, and crete the corresponding droplists of items.

Released in v0.6.8 . Closing.