Set window title to station title, so it's visible when stations drawer is hidden.
Display "Play" or "Pause", not "Play/Pause" in toolbar.
Playback window cleanup and Quick Look for album art.

- Use black-tinted NSLevelIndicator rather than NSProgressIndicator for track playback - eliminates distracting animation.

- Use NSButton with border on mouse-over rather than NSImageView for album art - cleaner and permits clicking, which summons Quick Look.

- Make control margins consistent.