cleaning up pom

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1542665 13f79535-47bb-0310-9956-ffa450edef68
CAY-1883 - Clean up Cayenne maven structure - get rid of aggregate modules

removing cayenne-server, will rename cayenne-core to server shortly

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1542666 13f79535-47bb-0310-9956-ffa450edef68