feat(login): add remember me functionality

- replace ngCookies by ngStorage: ngCookies only supports session
cookies; ngStorage supports both local and session storage
- add remember me checkbox in login.html and login.jade
- pass remember me parameter to auth.service in login.controller
- replace $cookieStore by $localStorage and $sessionStorage in
app.js/coffee
- replace $cookieStore by $localStorage and $sessionStorage in
auth.service.js/coffee
- add an expire parameter to signToken method in the server side
auth.service.js

Notes:
- $sessionStorage is used when « remember me » is not checked
- $localStorage is used when « remember me » is checked
- with « remember me » checked, the token will expire after 7 days

Closes #259 (partly)