WowAce

Hendrik Leppkes:
    - Add migration code for the new spell overlays
    - Don't register for events which are not used
    - Replace Blizzards OverlayGlow with our own to avoid potentially tainting the overlay glow storage.
    - Handle more events that require a button update
    - Update copyright header
    - Upvalue Lua built-ins
    - Fix variable name when assigning item links to buttons