Rich: change index naming scheme

This MR changes the naming scheme of loop and container indices to make them better distinguishable. Follow up from !1866 (merged).

• Change loop indices to e.g. iRing, iTrack, etc.
• Change associated container index received from event->GetIndex(...) to e.g. iRingIndex, iTrackIndex, etc.
• CbmRichRingTrackAssignIdeal, CbmRichTrackExtrapolationIdeal and CbmRichTrackExtrapolationMirrorIdeal need updates to support CbmEvent, added some TODO's