Allow users to access the Python Data Classes directly

[gaurav]

The Python Data Classes are currently generated in a single file at python/ccdhmodel.py. This cannot be accessed directly via pip.

I believe that the new LinkML model template currently being tested (#7) will provide this automatically, so we should probably try to implement that first and see if it meets our needs. If not, we will need to include a setup.py file that provides information on how to install the Python Data Classes. This will not only allow users to install the Data Classes via GitHub, but will also allow us to publish the Data Classes to PyPI, making it even easier for users to use them.

[sujaypatil96]

@gaurav: This issue can probably be closed, with the crdch model now accessible as a Python package that can be imported into our applications.