Support autoscrolling in puzzles

[jkenlooper]

Firefox web browser has a feature called autoscrolling that allows the webpage to scroll around when holding the third mouse button and moving the mouse. Some other web browsers support this by a third party extension. However, the puzzle page non-scaled view doesn't fully work with autoscrolling. It will only start autoscrolling if the click happens on the puzzle piece.

As an extra feature, there should be a way to map a key to do autoscrolling regardless of what browser is being used. This key could be held down and the mouse can then be moved to navigate the puzzle.