Video calling landscape changes to match specs

* Call card has 4dp corners, and is 90% visible
* Margins for call card
* Call buttons are center aligned with end call button
* Remote surface is always center aligned, tapping call card slides
it in and out
* Status bar is black

Bug: 19668216
Change-Id: Ifea27faa5f8ff32f6be13e777ca70aa4d0c7727e