Hide cursor over VM console

This PR fixes problem with duplicate cursor over VM console window. I've created a reusable CSS class "cursor-hidden" which can be used in other uses cases as well if needed.

Solution working on latest: 
* Chrome
* Firefox

It seems that actually Opera doesn't support needed CSS cursor property values, so we cannot remove cursor with pure CSS. I think the only possible workaround is to detect the moment, when cursor is entering the canvas and "leave" it outside - and attach to the mouse only if user moves cursor outside the canvas.

@RushPL maybe you know of better solution?