Better scrolling support

[rs22]

Using the scroll wheel, arrow/pgup/pgdn keys would make scrolling websites more convenient.

In addition, the scroll position should be reset to the top when a new site is opened, and reset to the last known position, when a site is re-opened from the "back"-button.

[radscheit]

@mewitte Your user story is already a known issue, so kill two birds with one stone :)