Phaser.Device - inverted from Game

The only known breaking change is if user-code relied on `device.game` or
manually called `checkFullScreenSupport`, as both have been removed.

- Phaser.Device is now a singleton object that does not belong to a
  particular game. The only thing that it belongs to is the window/host
  context.
  - `game.device` (shared between all games) and `Phaser.Device` are the
    same object.
  - There is no more `Device#game` property.

- The specific device-ready detection is moved out of Game into the Device
  code
  - It is possible for multiple Games (or even non-Games) to use
    `Device.whenReady`.
  - Initialization is done immediately upon device-ready; there is an
    onInitialized signal that is dispatched that can be subscribed to
    extend the default initialization.

- The fullscreen-detection code (that was the only dependent of game) now
  uses an new element.

- Updated jsdoc documentation