Switch to standard args4j parser instead of custom provided jar that mus...

...t be provided using fairy dust to maven.

Nice command line help:

$ java -jar target/johanna-1.0.0-SNAPSHOT.jar    --help
 --backend (-b) [MEMORY | REDIS] : The session storage backend to use
 --debug                         : Whether to log with DEBUG level
 --help                          : This command line help
 --host (-h) WERT                : The IP of the REDIS server to bind to (see
                                   --backend, defaults to 127.0.0.1)
 --identifier (-i) [MD5 | UUID]  : The identifier factory to use
 --port (-p) N                   : The TCP/IP port to bind to


... maybe you take a look on this. I think it's 
* less boiler plate code (the setters), 
* makes things more private
* reduces cumbersome dependencies and 
* has some documentation.

Now that you introduce an enum, I think it'd be good to get rid of the switch-block at this place alltogether (make these enums behave like factories).