Controls as Neighbour Canvas

This makes controls canvas appear in the DOM next to player canvas, instead of always being attached to document `body`. It solves (or should solve) scrolling and resizing issues and frees us from listening for scrolling events all the time. 

Regarding styles: I don't want actually to wrap both canvas with additional `div`, since it may break the styles user previously added to player canvas. I've fixed the very most of the positioning issues, including calculating border-width and margin of player canvas to shift controls' canvas, but still there's a small but stable shift in one-or-so-pixels both from the top corner and from the left corner, don't know why for the moment.

Hacks used:

* set `position: relative` and `bottom-margin` equal to negative player height for controls canvas, to make them appear just above the player (`position: absolute` does not helps to get rid of pixels mentioned above)
* manually set `vertical-align: top` for both canvases, since `canvas` element has `display: inline` and `vertical-align: middle` by default, which causes a bottom margin for canvas (setting `display: block` does not helps to get rid of pixels mentioned above)

Also:

* removed scroll and resize listeners since they has no meaning anymore (and it's good)

@skavish @mcm69 @Animatron/website plz review.