[maven-release-plugin] prepare release cayenne-parent-3.1RC1

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/branches/STABLE-3.1@1566167 13f79535-47bb-0310-9956-ffa450edef68
[maven-release-plugin] prepare for next development iteration

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/branches/STABLE-3.1@1566169 13f79535-47bb-0310-9956-ffa450edef68