Tweak animations to use the (Slightly slower) android default animation speed.

Remove the fadeout to make things look a little less weird
Make the animations slide in from the edge. (See the aforementioned comment about jankyness)

TODO: don't remove the message view until _after_ the animation runs. Before HC, that requires rather a lot more code (writing a whole animationadapter) than it should.

TODO: get the messageview to stop jumping to hide the header area as it's displayed.