UI updates to sample

1. Updated CardPresenter to not set a background color onCreate. (this was showing up blue and then gray when the card loads) the right way to do this is onSelected method (also added this)

2. Modified themes.xml to display colorPrimary when the app launches

3. PlaybackOverlayActivity is calling overScan() method onCreate. The method was adding a big fat border around the layout. Not sure why we're doing this. I commented it out and it works fine on my end. Didn't remove because I'm not sure if we really need this.