Update Cast Instructions Overlay display

- In iOS 8 we have UIModalPresentationOverFullScreen, so we will use
  that instead of the custom transition (which did not work well on
  iOS 8). For iOS 7 this will result in a solid background, which
  still looks reasonable and conveys the right information.
- Update preview images to aspect fill to avoid distortion in scaling
- Center Y on ipad activity indicator when casting
- Add version display in cast menu
- Fix a bug where casting over a current cast may result in a crash/bad UI
- Fix a bug where tapping minicontroller in another video info screen cast
  that video.
- Make playing a local video clear the last session information.
- Fix constraint issue with ipad casting view.
- Fix z ordering issue with volume control on iphone castinv view.

Change-Id: Ic80e7d4de8b0ddfe05153ded494ff25c602aff83