Allow definition of typed relations in templates types

[DirkMahler]

Currently typed relations may only be used between types with explicit labels. It shall be possible to specify typed relations in templates, e.g.

public interface Template1 {
  TemplateRelation getTemplateRelation();
}

public interface Template2 {
  TemplateRelation getTemplateRelation();
}

public interface TemplateRelation {
  @Outgoing
  Template1 getTemplate1();

  @Incoming
  Template2 getTemplate2();
}

@Label
public interface A1 extends Template1 {
}

@Label
public interface A2 extends Template1 {
}

@Label
public interface B1 extends Template2 {
}

@Label
public interface B2 extends Template2 {
}