Speed control refinements

When dealing with multiple clips, the speed control system is pretty cumbersome. Sometimes people want to easily slow down a cut together animation sequence.

It would be nice to be able to select more than two clips and simply type in 0.5 to drop it down to half speed and have Blender's video editor automatically re-size and shift all of the clips to match (as well as automatically increase the project frame range to fit) -- while preserving all fades and transitions.

For examples of this type of thing in action check out a few of the other video editing apps, like SpeedEdit.