How to install the Appengine SDK to the Maven local repository?
Note that this needs to be done only once.
  $ mvn gae:unpack
  Note that you don't need to manually download any SDK.

How to generate the WAR?
  $ mvn package
  $ mvn war:war
  Note that this must be done before running the webapp locally and before
  deploying it to Appengine.

How to run the webapp locally?
  $ mvn gae:run

How to deploy the webapp to Appengine?
  $ mvn gae:update
