Dsl spec interfaces

```
node_types:
  some_type:
      interfaces:
          interface1:
            ...
          interface2:
            ...
node_templates:
   some_node:
      interfaces:
         ...
      relationships:
         - type: ...
           target: ...
           source_interfaces:
             ...
           target_interfaces:
             ...

relationships:
   some_relationship:
       source_interfaces:
         ...
       target_interfaces:
        ...

```