Remove explicit repository OSS Sonatype from POM
Move common dependencies into parent POM
Version bump dependencies in graylog2-server POM

The Maven versions plugin (http://mojo.codehaus.org/versions-maven-plugin) can
be used to check for new versions of dependencies or updates:

* http://mojo.codehaus.org/versions-maven-plugin/examples/display-dependency-updates.html
* http://mojo.codehaus.org/versions-maven-plugin/examples/display-plugin-updates.html