With this changeset the spring servlet configuration is separeted from the
application configuration. This will result in a main context and a servlet
context, holding only spring mvc information.

This change has a very nice side effekt: Spring AOP beans will be loaded
only once in application context, not a second time in mvc servlet context.

This checks if there is a user in current security context. If not, an
UnauthorizedException is thrown which will result in HTTP - 401.

* @ResponseBody Annotation for JSON Response
* Old ARSnova Servlet does nothing
* New Spring Servlet loads Beans, Services, Security and SocketServer
* One Property Loader which is used in XML Spring Configuration and with
@Value Annotation

With this configuration both
 - spring security setup
 - bean properties
will be set to values defined in /etc/arsnova/arsnova.properties.

Admins ARE REQUIERED to create production settings file by given example
in /etc/arsnova.

properties loaded from local filesystem

remove websocketcontroller and let sessioncontroller do the
authorization
add toString to User entity

Properties from properties file are available in all beans now.
CouchDB connection in SessionService will be created using these settings.
If a connection fails, the next request will have a new try instead of
throwing an exception.

switch to oauth2 authentication which allows facebook, twitter, google
etc authentication

include config.properties.example and let override values by
config.properties
cas spring security configuration adjustments