Correctly state guest authentication

The API returned "ldap" instead of "guest" for guest authentication
before.
Make authentication providers configurable
Fix use of deprecated class
Implement CouchDB based user management
Implement DB authentication and make LDAP login RESTful
Add mail address filter and send activation mail
Move user account actions to seperate controller
Add delete action for user accounts
Fix XML configuration
Add javax.mail dependency
Fix mail encoding
Temporarily ban users by IP address after reaching failed login limit