Hopefully fix unhandled_response failure.
Move response structures to a DSL.

This should make things slightly more compact, and the DSL can hopefully be
reused for BAPS3.
Rearrange codes table, add MOVE_ITEM_IN_PLAYLIST.

This is currently unhandled, but now has a structure.

I'll be adding all known BAPS codes into the codes table shortly.
Split and fill out code table.

The functions for looking up code symbols have been moved to a DriverCommon
module, allowing the code table to contain only codes.
Fix client change messages.

These aren't actually two separate commands in BAPS!
Start implementing move-item-to.

This includes the response handler and some changes to the model objects APIs
to allow it to work properly.

Note that adding an item to a ListModelObject now behaves like inserting into a
list, not overwriting the existing ID.