Template generator should support multiple inheritance

[dvojtise]

The template generator that generates aspect from an ecore file currently supports single inheritance only (. (new K3 project, next, select User Ecore Basic aspect template ) since we now have a syntax for supporting multiple inheritance (using the with attribute), we should enhance this generator to use it. (see. http://diverse-project.github.io/k3/publish/user_documentation/html_single/user_documentation.html#_extending_an_aspect_multi_inheritance )