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.

This refactors the filter guide docs into a single file.
Also removes out of date references to the fact that Angular used to enhance Arrays while evaluating expressions.

We have links to better videos now on the guide/index page.  This one's time has past.

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.

When navigating to URLs such as
docs.angularjs.org/api/ng#filter, the browser
was not able to navigate to the named anchor,
"filter," because the anchor did not yet exist
in the DOM.

This fix uses the $anchorScroll service
to automatically scroll to the right place when
the content has been added to the page.

Fixes #4703

Fixes some warnings during docs generation.

Closes #4673