feat(docs): adding the <doc:protractor> ngdoc-tag

This is the first step in migrating tests from <doc:scenario> to <doc:protractor>.
In-documentation examples with doc:protractor sections will have their contents
output to a tab on the docs site as well as output to a standalone test file in
build/docs/ptore2e.
fix($httpBackend): Allow status code 0 from any protocol

Android 4.1 stock browser also returns status code 0 when
a template is loaded via `http` and the application is cached using
appcache.

Fixes #1356.
Closes #5547.
chore(build): add relase-after-cdn script