Enable full screen mode for 2D browsing

[haanhvu]

Fixes #1494

Add a "Fullscreen" item in the hamburger menu to set the current window in the fullscreen mode. This item will not be available in kiosk mode.

[svillar]

Seems a nice feature, however I am not sure it's polished enough. At least I found weird the following scenarios

1. put the browser in fullscreen
2. goto youtube.com and select a video
3. in the video player click on fullscreen
4. exit fullscreen

When you exit fullscreen the browser goes back to the unfullscreen mode again. I don't think that's neccesarily bad, but the addition of this feature makes the navigation confusing, it's like the fullscreen mode you had previously selected was "forgotten". In the current code, it's crystal clear, the window goes fullscreen only when the page requests it (after a user gesture of course).

Another example is when after clicking on a link the page opens another tab. In that case the window un-fullscreens automatically as well, giving the impression that the feature no longer works.

I am not really sure what to do. Maybe @felipeerias has further thoughts about how the UI interaction should work in this case but I think it's really tricky if we want to make it work properly.

Apart from that the commit message should be changed. In general it should follow this template:

Brief description/Title

Detailed description

Fixes #0000