Finding and registering the classes implementing the translation

The generator for HOT is designed as follows, in similar fashion to the Heat resources. Each TOSCA type has a separate translator class to implement the translation. They are derived from the HotResource class (hot_resource.py). They are kept in 2 designated directories, one for the base type and one for the custom type. This allows for new TOSCA node type to be added without changing the existing code base
In the current code, this set of classes is coded as a dictionary in tranlsate_node_template.py for expediency. This should be changed to a registry that checks for the 2 directories above for available translation classes when the translator is run.