The old script, being already used in Google-managed CI, continues to
deploy poms with com.google groupId. A new script,
maven/push-gwtproject.sh, has the same contents as the old one used to
have, and deploys the org.gwtproject poms.

Samples that use maven have also been updated to use the new ltgt gwt
maven plugin and the new groupIds.

Change-Id: I0f582304faf9546ac37616a78bc7735f8beeba26