The current Show Glow actions (OnShow+Conditions) only supports the old Blizzard Glow, we should add the new glows to that.

Additionally we currently only allow specifying a static frame. This could be extended to be as flexible as the Attach to Frame feature, in allowing glowing a unit frame/nameplate or a custom frame.

This would enable creating glows on e.g. group frames, which are quite popular.