Updating the animation page.

This is an attempt at slowly updating the introduction to animation page, as per T10344.

• Introduce beginning animators to the idea of an animation pipeline.
• Point people at all the separate components.
  • Timeline docker
  • Animation docker
  • Onion skin docker
  • Animation curves
  • Am I missing something?
• Update the walkcycle tutorial.
  • For this I would really like to be able to have the animation cycles in, but that's probably gonna take a while...