Seek bar polish

Items:
 - use proper style
 - align left and right sides of seek bar with other elements
 - still show bar when progress is disabled

Bug: 150724977
Test: manual - play music and look at seek bar
Test: manual - play iHeartRadio for example with progress disabled
Test: manual - play spotify which has seek disabled and check style
Change-Id: I340df584ae4dfa0331eedd0e9fd20fcec19ba8da