Fix component dragging on a pushed page

There are three viewport types with a fixed width: Desktop (by default 1280px wide), Tablet (by default 720px wide) and Phone (by default 320px wide). If a user selects any of these viewport types, but his browser is not wide enough (e.g. he chooses Desktop on a browser of 1000px wide) the channel is still rendered at the selected width (e.g. 1280px) and a horizontal scrollbar appears. In that case, dragging a component to another container should scroll the channel horizontally when the user hits the left and right edge of the channel manager app (just like the channel scrolls vertically while dragging a component when you hit the top and bottom of the app).

Note for QA: just like with vertical scrolling, the code has a different implementation specifically for Firefox. So please verify this on all supported browsers.