Allow redirect rules to be ordered via drag'n'drop

[acelaya]

Right now, the only way to order a rule is by clicking its up/down button, which can be cumbersome if you want to move it several places.

The buttons need to exist, for mobile devices and for accessibility reasons. However, that could coexist with a mechanism to drag rules in order to sort the list.

Additionally, there's a couple extra improvements that could be applied:

• When clicking the up/down button of a rule, keep it focused so that it can be consecutively moved by pressing Enter/Space consecutive times.
• When sorting via up/down buttons, reorder with an animation, otherwise the result is sometimes too subtle to know if it worked.