Remove dead code.
Match HUD UI via type introspection.

This allows HUDs to display properly for subclasses.
Fix HUD line scanning.

Currently, HUDs piggy-back on ACE code folding. Due to what  I suspect
is deferred UI rendering by ACE, the check used to detect code folding
was too strict.
Fix HUDs losing state upon code edits.

Instead of scanning no HUDs and deleting them (old behavior), I've
instated the hacky solution of hiding all HUDs until the code is parsed
again. It'd be good to replace this with faster HUD repositioning
someday.