Chat Better

Fixes from the first round of feedback.

FIXED
- Action bar messages no longer end up in chat. They were being mirrored into
  the chat log, so mods that animate that text letter by letter (Diversity's day
  counter, countdown timers) produced one chat line per letter. Thanks Ludafa.
- ChatHeads: Chat Better draws the chat itself, so ChatHeads' player heads never
  got a chance to render. They are now drawn by Chat Better instead - see
  Settings > Chat > Player heads, on by default when ChatHeads is installed.
- Emoji with no artwork on your system are no longer listed in the picker as
  broken tiles. Thanks songmoth.
- Opening an image full screen is no longer blurred, and large images are now
  shown at full resolution instead of the small chat copy.

ADDED
- Player heads beside messages (Auto / On / Off)
- Merge repeated lines - an identical repeated message collapses into one entry
  with a counter, instead of filling the chat
- Toolbar position: Above input / Screen top / Hidden, so it can be moved clear
  of the command suggestion popup
- Hide unused buttons - switching a feature off now removes its icon
- hiddenMessages in config.json - a list of text that should never reach chat
- emojiExcludedCodes in config.json - shortcodes Chat Better leaves alone, so
  another mod's emoji system (Figura) can claim them