Add snapshot plugin repo to jclouds-project

It's needed by downstream projects such as labs-google and labs-openstack. The commit changing the modernizer config is needed to allow jclouds-project to compile.
> hmm.. how will this affect projects that import this, such as labs?

This is in the `jclouds-project` project, which should **only** trigger in jclouds/project. All other modules (in jclouds/jclouds and other repos) should inherit from `not-jclouds-project`, which gets the config files from the classpath via a jclouds-resources dep.