Compositor animations - actual

There are both some good changes and some terribly hacky changes in this
commit.

- Server uses a different struct than client now for windows, so
  arbitrary compositor things like effect parameters can be added
  without having to rebuild everything. That's good.
- Client window structs no longer attempt to track or use window
  locations. That's good.
- Windows do not destroy in response to the destory command, but rather,
  a special animation is triggered; the end state for this animation
  calls the actually window destruction code. That's a hack.
- Animations are based on rendered frames, not on time. That's a hack.