chore(docs): replace "Edit in Plunker" button with Angular Material

Closes #10305
docs(app): minor refactoring of 'docs/app/src/*'
docs(app): refactor the Docs App based on the MD prototype

I incorporated the prototype detailed in https://github.com/gkalpak/angular.js/issues/3.

Things that are different from the prototype (besides using actual data):

 * The left sidenav (toc) is not styled properly (or even readably).
 * The subheaders in the left sidenav are not "stickying" properly (only `ng` becomes sticky).
 * Icons are missing (since we are not using FontAwesome). E.g. search-fab, toc-toggle, results
 * In the right sidenav (search) there are some unwanted horizontal scrollbars.
   (This section probably needs rethinking anyway.)
 * I have implemented a `responsiveMenu` directive to show the options in the header-menus
   (Learn/Develop/Discuss). The purpose is to show the options in a "dropdown-ish" menu on larger
   screens and using a BottomSheet on smaller. At the moment a BottomSheet is used on every
   screen-size.

Notes:

 - Still no version-picker and breadcrumbs (I have left the original implementation of those two
   commented out).
 - I have replaced the previous docs.css with a new one containing the style of the prototype.
   I have renamed the old one to `docs_old.css` and left it there temporarily for quick reference.
   We need to clean up this and the rest of the old CSS files.
 - The main content area is totally unstyled and needs some love (a lot actually).

I have also "sprinkled" the code with a few more TODOs/FIXMEs.

(For more details on known issues and missing features take a look at
 https://github.com/gkalpak/angular.js/issues/3)
docs(app): fix styling of left sidenav, add FontAwesome

Since the structure was a little different than the prototype,
classes/styles where not applied correctly to the links in the left
sidenav. This commit fixes the issue.

I also added FontAwesome, in order to be able to display icons until the
Material Design icon-font is released. Since this is a temporary meassure,
I didn't added as a bower dependency; just added a `font-awesome` folder
in assets and added `font-awesome/css/font-awesome.css` to the stylesheets
of each deployment (under `docs/config/services/deployments/`.
docs(app): make tests pass

Due to the recent changes ragarding the Docs app "Materialization", some
tests where failing for the following reasons:

1. JQuery wasn't being copied to 'build/docs/components/'.
2. E2E examples 89 and 90 were relying on the Bootstrap's glyphicons.
   Temporarily replaced with FontAwesome icons; to be replaced with
   Material Design iconfont, when ready.
3. `ngMaterial` (and its various dependencies) weren't loaded by Karma
during unit testing (causing modules depending on it to fail). Added a
fake `ngMaterial` module (as a temporary solution).