Although demo apps run in an isolated environment, we need to be able to tell them to disable
animations when we are running end-to-end tests.  By sharing the same instance of $animate
between the two environments we can disable animation across the board.

The $animate service uses the $$postDigestQueue to run animations.  The outer $animate
service uses the outer $$postDigestQueue and to queue up these animations.  This means that
when we run a digest inside the embedded scope, the animations are never performed - they
just sit in the outer scope's queue and are only run when a digest is run on the outer scope.
By sharing this queue across the two scopes the animations are performed correctly.

Before, there we multiple overview docs:
- guide/overview
- guide/introduction
- guide/dev_guide.mvc
- guide/dev_guide.mvc.understanding_model
- guide/dev_guide.mvc.understanding_view
- guide/concepts

Now we have:
- guide/introduction: High level description of Angular with the key benefits but without code or any concrete concepts
- guide/concepts: explains all important concepts with a simple example and contains deep links to the other parts of the guide.

 All the old information was moved into existing documents or deleted when they were duplicates.

code prettification is expensive and not needed for e2e tests, so I'm disabling
it to speed up the e2e test suite.

this is a temporary measure, see previous commit for more info.

This is necessary to make e2e tests pass for implementing #3411. At present, the docs are violating the rule being enforced by double-bootstrap prevention.