Update inline playback button to material design (#4104) #4106
This PR addresses my feature request in #4104.
It replaces the old gingerbread-styled inline playback icon with a more modern design. The new icon is based on ic_play_arrow_48px.svg which is part of the official material design iconset (license:CC-BY 4.0) .
To account for darker card backgrounds I flattened the icon, as suggested by @hssm.