Feature/logout

added an user account provider to load user account details
created user domain model
add backend route for getting those account informations
add directive to show username and logout button in nav bar
eMail <-> email
also the same with firstname etc.
the constructor should not be a "conversion" service.

one approach:
 - create an empty user: `var user = new window.User()`
 - call a convertion method on it: `user.setDataFromXXX()`
 - (if you send the data back to the server, we may have to convert it again)

second approach:
 - do not rename the variables