Roleplay Event Helper

Fixes the minimap button sitting inside the minimap's border, on top of the map.

- The orbit radius was a fixed 80 pixels, which is only correct for a
  140-pixel minimap. The retail minimap is larger, so the icon was drawn well
  inside the ring. The radius is now measured from the minimap itself, so the
  button rides the edge at any minimap size or UI scale.
- The button follows the minimap when it is resized afterwards, instead of
  keeping the position it was given at login.
- Square minimaps (SexyMap and several UI packs) put the button on the
  square's edge rather than on a circle they do not have.