Comment out maven-idea-plugin, maven-one-plugin and maven-model-converter. Mark them as retired.

git-svn-id: https://svn.apache.org/repos/asf/maven/sandbox/trunk@1631212 13f79535-47bb-0310-9956-ffa450edef68
Add SCM URLs, to make the links to the sources on the site in Jenkins correct.

git-svn-id: https://svn.apache.org/repos/asf/maven/sandbox/trunk@1631225 13f79535-47bb-0310-9956-ffa450edef68
Ignore IDEA directory.

git-svn-id: https://svn.apache.org/repos/asf/maven/sandbox/trunk@1631226 13f79535-47bb-0310-9956-ffa450edef68