Shared reference definitions

[novoj]

It would be nice to have possibility of "global references" similar to "global attributes". In other words to have a way for defining shared reference definitions, that could be reused accross multiple entity type definitions. When the global reference definition changes, the change would be automatically propagated to all entity types that use this shared definition.

This feature would allow maintaining repated references nicely and also would open a chance to provide same covering interface in generated TypeScript classes / types.