More CSS changes
* Introduce media querie for < 480px
* Adjust new issue form with mq<480px
* Add styles to links
* Remove 'UTC' from creation dates of issues and comments
Separate current issues index in two. Other minor changes
* Place sign in user form in header inside app layout
* Divide current home controller in 2 (one before login and another after)
 * Modify redirection path after sign out
 * Redirect to home index in issues index when no user signed in
 * Redirect to issues index in home index when user signed in
 * Decorate plate in header