Use a central attribute for animation speed

Several people have complained that animations are to slow or want to turn them off completely, so I tried how things would look with faster animations and I am personally not sure that a faster speed is an improvement. Things seem very hectic and it becomes more apparent how slow Briar is loading stuff from the DB. Also, other animations like the navigation drawer opening now seem slow compared to our animations.

What could be considered an improvement is that this MR centrally defines our animation speed in one attribute. So I did that and used our old speed.