Feature/107 add login functionality

feat(auth): introduces authentication functionality:
- if user is not logged in he is allowed to public states only (see app.js isStatePublic())
- http interceptor is set up to all api calls to logout user if api returns 401 (it is to prevent the case when user got logged out by the back-end, but did not reload page in browser)
- formInputValidate directive added to allow nicer forms validation in UI
- savedLoginForm directive takes care of the case when login form is being prefilled by a browser
- exit button in a footer is a logout now
- footer is different for logged in and anonymous users