Pulled LLDropTarget into its own files and brought in the callback version so we can use either, whereever we need them, without rewriting them.
This makes code for drag and drop items into boxes easier.
--------Auto-Response--------
Added item box to Adv. Chat, finally you can send autoresponse with item!
Taught to LLViewerMessage to understand this.
------------Build------------
Added in comment labels for more sections of system preferences.
Everything new in the System->Build tab will reset on cancel, except the item, I see no reason to reset an item.
Added in BuildPrefs, and settings like them.
Taught LLToolPlacer how to give creations material type, and size, and ask importtracker to do the rest.
LLViewerObjectList now pings importtracker whenever it notices newly created objects that are ours entirely, so we can exact our will upon them.
Cleaned up most of importtracker code so we can use only the parts we need, and do it well.
Added ObjectPhysicsProperties to message.xml
