add new animation type for MMST

Fixes animation erros and invisible mist when slaying vampires in BG2.
only reenable spawns when the party has moved away some

If the spawn point is just out of sight it often respawns immediately,
attacking the party that is moving away from it from behind.
don't mess with ItemInfoWindow if we go straight to ItemWindow

Fixes a Python error when opening a container.
be less strict when initiating dialog

Requiring line of sight can easily break some of the game scripts
when the party is positioned in a way that keeps some members
invisible. I've seen it break both BG1 and BG2 in places.

It also means that if "the party" sees someone you'd like to talk
to but the party leader himself doesn't, clicking on the target
won't initiate dialog.
don't auto-identify items when they are put in a bag
get rid of duplicated item creation code
try harder to find items to aggregate in shop listings

Many items that don't use charges (e.g. weapons or armour) come
with bogus charges, and if the shop fails to take that into account
there'll be mutiple listings of those items in the item list.
share item sanitation code between item loading and creation

Also use it for shops.