macosx: Redesign library view playback control bar

Per our discussions, this library playback controls bar is much smaller and more space efficient than the previous iteration.

This is intended for use when browsing the library and playing music, not for in-video playback controls -- we will be moving to a larger overlay-style control bar there

With changes:

Prior to changes:

Signed-off-by: Claudio Cambra developer@claudiocambra.com