dvdplayer: improved dropping control

In order to maximize performance frames need to be queued in renderer (we already do this) and hw decoders. If we request a drop in decoder, the time video catches up will not show at output stage immediately. Currently player does not take this delay into account and drops more frames than required which results in noticeable drop of quality in particular when windows are opened during playback. (number of render buffers should be bumped as well -> different pr)

@elupus for review please