Add basic classes for use case tosca_compute_only

Assumption:  inputs to the tosca template are given at the translation time, so all references to the inputs are completely resolved
in the intermediate representation of the tosca template
This get_input resolution is not implemented yet, so for now test with tosca_compute_only_resolved.yaml, which does not use get_input in the template

Need some more fine tuning in the generated HOT template