added gs-geogit dependancy to geonode. It is on gs-geogit 2.5-SNAPSHOT since repo doesn't have 2.5.1 available at http://repo.opengeo.org/org/opengeo/geoserver/gs-geogit/
Merge pull request #23 from smesdaghi/master

added gs-geogit dependancy to geonode. (2.5-SNAPSHOT vs 2.5.1)