[Confluence] - some code improvements for VideoOSD

makin use of a grouplist instead of separate button controls.  this way navigation and button placement doesnt have to be handled manually.
Saves quite some code and should be less prone to errors when it comes to any future adjustments to this dialog.
Also removes three empty id declarations ( id=""), not sure how those made their way into code.

Normally I wouldnt really care about this stuff for any other skins except my own ones, but since confluence is used as a base for lot of new skins I think it makes sense to get the base structure in a sane shape. 

@ronie and @BigNoid for review.