Backend: Optimize main menu for Chrome.

Moved main navigation menu to separate GPU layer on WebKit based
browsers to avoid unnecessary repaints.
Collection: Window system: Put windows on separate GPU layers.

On WebKit browsers force placing windows in separate layers. Aside
from making redraws 3-4x faster unnecessary repaints are also avoided.
YouTube: Use json_encode instead of built-in function.
YouTube: Change theme of video preview.
SwfObject: Use json_encode instead of custom function.