Add Document class for Regulations3k

[alexm118]

Adds the model for our regulations3k document that we search on. This will allow us to create and index all regulations in ES7.

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Additions

• SectionParagraphDocument - Represents the data we load into elasticsearch for regulations.

How to test this PR

1. Inside the python container of our local docker stack run cfgov/manage.py search_index --rebuild -f and all regulations are loaded into ES7 index regulations3k. Can be confirmed via the kibana dashboard.

Checklist

• PR has an informative and human-readable title
  • PR titles are used to generate the change log in releases; good ones make that easier to scan.
  • Consider prefixing, e.g., "Mega Menu: fix layout bug", or "Docs: Update Docker installation instructions".
• Changes are limited to a single goal (no scope creep)
• Code follows the standards laid out in the CFPB development guidelines
• Future todos are captured in comments and/or tickets
• Project documentation has been updated, potentially one or more of:
  • This repo’s docs (edit the files in the /docs folder) – for basic, close-to-the-code docs on working with this repo
  • CFGOV/platform wiki on GHE – for internal CFPB developer guidance
  • CFPB/hubcap wiki on GHE – for internal CFPB design and content guidance

[willbarton]

One quick comment, but I love how simple and readable this is.

[higs4281]

Would we want Django's TestCase here instead of unittest?

[alexm118]

Good Question, I hadn't considered the differences but upon some research I don't think we need Django's TestCase:

Using unittest.TestCase avoids the cost of running each test in a transaction and flushing the database, but if your tests interact with the database their behavior will vary based on the order that the test runner executes them. This can lead to unit tests that pass when run in isolation but fail when run in a suite.

This doesn't rely on a database, we are just defining the class and preparing the document in memory, so I think unittest.TestCase makes more sense here

[higs4281]

One nit suggestion.

[higs4281]

I'd like to do some more testing of Haystack operations.