fix(ngdoc.js): update default directive @restrict to 'A' + add appropriate docs for ng.directives

The default restrict of a directive has been changed from `AC` to `A` awhile ago (and the guides have been updated to reflect that). 
But `ngdocs.js` still has it's default restrict set to `AC`

This generated a lot of wrong documentation, like [ngShow](http://code.angularjs.org/1.2.0rc1/docs/api/ng.directive:ngShow#Usage), where it's stated that it can be used as `AC`, when it's actually just `A` ([plunk](http://plnkr.co/edit/jRRqNuO1ikoTae0pv6kt?p=preview)).

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This PR fixes the restrict in `ngdocs.js`. It also adds the correct `@restrict` to directives that need it.

Since I was fixing the usage of directives, I also fixed the `ngChange` usage, and simplified the `restrict` declaration of `form/ngForm`, all separated in their respective commits.


I've signed the CLA as Rodric Haddad