chore(ngdoc): add dynamic anchors to anchor list

Fixes some warnings during docs generation.

Closes #4673
docs(guide/directive): link to directives API from the top of the page
fix(docModuleComponents): implement anchor scroll when content added

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
chore(docs): specify how ngClass deals with natural CSS transitions
docs(guide/overview): Refactor overview and mvc docs

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.
chore(docs): add -webkit-transition for ngClass example
docs(guide): delete ancient video

We have links to better videos now on the guide/index page.  This one's time has past.
docs(guide/filter): Refactor filter guide docs

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Also removes out of date references to the fact that Angular used to enhance Arrays while evaluating expressions.