The add repository command should support IdClass

[ivannov]

At the moment the add repository command supports creating entities with simple primary keys, i.e. annotated with @id. However JPA provides the possibility to have compound IDs, where a class is annotated with @IdClass and then a field of this class is used as primary key.

The command should support that scenario as well. For more information on how to implement it, check the Forge mailing list discussion:
http://lists.jboss.org/pipermail/forge-dev/2015-August/004313.html