exports-v2 - Updates from image review

[shapiromatron]

I reviewed around 3000 visuals and found very minor differences in <1% of them. This PR addresses fixing the issues in that 1%, along with a few other bugs I found when investigating these differences. Here's a detailed list of changes I made:

• The data pivot html view previously didn't appropriately handle a 500 error on a dataset and treated it like a valid response; this is now fixed and it throws an error message correctly
• The animal treatment_period transformation method didn't appropriately transform text in a few cases; this was rewritten
• In some cases, if a rare case where the study evaluation metrics have duplicate names, an export would fail because you can not assign multiple columns (df.loc[list_of_strings]) if columns are not unique; a get unique name method was added, and the study evaluation fetching code was updated to be reused across exports
• If data is correct and upper and lower CI are not provided, epi can calculate upper and lower ci values. A new method was added to do so
• Fixed invitro category addition to a datafarme where an endpoint has None as a category ID
• Remove iv_endpoint-category_id from invitro data pivot exports

Unrelated change:

• Fix deprecation warning when running pytest (in conftest.py):
  • Marks applied to fixtures have no effect
• Add UDF API to the openapi yml specification

[rabstejnek]

Changes look good! I had just one comment about a TODO left in the code, after that is addressed I think its good to merge.