nametags now track avatar head
avatar_skeleton now loaded as param block
vector3 param block parsing support
fixes for param block recursion

object inventory offers don't increment system menu count
added customizable merging behavior for duplicate "unique" notifications
fixed overeager notification channels

phase 2, removal of extraneous signaling in favor of llnotificationchannels
made notificationchannels work better with overrides and lifetime managed
by creator

fixed crash on login

phase 1, removal of most of llnotificationhandler

  "InventoryOutboxLogging" debug flag.

removed merchant outbox context menu
reviewed by Leslie

reviewed by Leslie

Use the new "Avatar Rez" debugging tag to see the output.