[NEXUS-7768] Replace Kenai modello config with a capability

https://issues.sonatype.org/browse/NEXUS-7768
http://bamboo.s/browse/NX-OSSF436

In addition to using capability for configuration I refactored Kenai impl to be similar to how Crowd is implemented regarding configuration. Some methods do not make sense now but will be used when we will add  an UI