Port classes in classes.ts to python

[jon-myers]

This is a project that JM and Shreyas will work on. This will be useful for users and researchers (including in our team) to write python code that can get information out of our transcriptions. This way, we will be able to write python code to do computational analysis, and visualizations. Potentially, this could mean complex process could take place on the server, with resultant images / data being sent back to the browser, instead of having to do everything in the browser.

[jon-myers]

Plan:

1. Set up a new branch.
2. Write tests in python.
3. Give Shreyas an opportunity to try to write a class (maybe for Pitch?). We will know it is successful if it passes all the tests.