chore(doc-gen): implement dgeni

End 2 end tests wait for all `$timeout`s to be run before completing the test.
This was problematic where we were using timeouts that restarted themselves because
there would never be a point when all timeouts had completed, causing the tests to hang.

To fix this $timeout had been monkey-patched but this caused other issue itself.

Now that we have $interval we don't need to use $timeout handlers that re-trigger the $timeout
so we can ditch the monkey-patch.

This commit tidies up any examples that are using this approach and changes them to use $interval
instead.

Closes #5232

jQuery's elem.html('') is way slower than elem.empty(). As clearing
element contents happens quite often in certain scenarios, switching
to using .empty() provides a significant performance boost when using
Angular with jQuery.

Closes #4457

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.