get_model_version() does't load module

[chrisdicaprio]

Currently NshmModel.get_model_version() loads the model definitions as modules. This is a problem if a user calls get_model_version(), modifies the model object, and then calls get_model_version() again, the modifications will effect the second call of the function. This is because the python importer does not re-import a new copy of the module.

We should be able to define models as a dict of args to be passed to NshmModel() rather than the object created in the model version moduels themselves. Will likely require removing slt_config from the NshmModel class (#97 )