Fix rendering issue on error in forgot password page

#### Story ####
- https://www.pivotaltracker.com/story/show/68935910

#### Note ####
- ~~moved previous style fix for account registration and edit pages into <code>mixins.less</code>~~
- ~~added new <code>devise_error</code> mixin to login and registration classes, resolving the rendering issues on input errors~~
- added <code>field_with_errors</code> outside login.less' namespace
- left origin usage of <code>has-error</code> in registration styles to overwrite <code>required</code> style