added missing server-plugin.xml
added missing server-plugin.xml

nachivpn/neo4j-gremlin-plugin,thinkaurelius/neo4j-gremlin-plugin,thinkaurelius/neo4j-gremlin-plugin,nachivpn/neo4j-gremlin-plugin,kangkot/neo4j-gremlin-plugin,kangkot/neo4j-gremlin-plugin