JAVA: Add Maven support for the libphonenumber demo.

JAVA: Add Maven support for the libphonenumber demo.

That lets the demo be part of the libphonenumber Maven project thus adds the following benefits:
   - Automatically update the version of the demo and the libphonenumber artifact the demo depends on when performing a release.
   - Let Maven handle the deployment of the demo to AppEngine without any need to install the AppEngine SDK.
   - No need to push the dependency JARs (servlet, apache common fileupload/io) even if they are still here to let you use Ant if you prefer.

Note that this CL depends on CL 5395054.

Review URL: http://codereview.appspot.com/5405041

git-svn-id: http://libphonenumber.googlecode.com/svn/trunk@409 ee073f10-1060-11df-b6a4-87a95322a99c