Merge pull request #527 from gbeatty/ViewportQuad

Added show property to ViewportQuad
Merge pull request #529 from gbeatty/video

corrected typo when removing video element from the document body
Merge remote-tracking branch 'origin/master' into video
more videos
removed old videos
Merge branch 'video' of https://github.com/gbeatty/cesium into videoWithOverlay
removed test code
manually remove `seeked` event from old video to prevent multiple seek loops from running against subsequent videos.
Merge branch 'video' of https://github.com/gbeatty/cesium into videoWithOverlay
test files
removed videos temporarily
switched to high fidelity terrain server