[WIP] Everypolitician::Positions prototype

[chrismytton]

What does this do?

This pull request is a prototype of an Everypolitician::Positions class for interacting with position data.

Why was this needed?

We want to add cabinet data to the term pages and in order to do this we need to interact with the position data from everypolitician-data. This data is currently in the unstable directory of each legislature, and therefore isn't available from the everypolitician gem yet.

Relevant Issue(s)

• Add method for accessing legislature position data Add a way to get cabinet membership data for a person #15606

Implementation notes

I think I've actually got two changes going on here:

• Adding classes for interacting with position data
• Adding a class for getting position data from a CSV

So I think I probably want to end up with one pull request which adds the Position and Positions classes, and then a separate one that adds the UnstablePositionCSV class which can then return an instance of Positions. Then when we decide on where we want the CSVs to live we can just switch out UnstablePositionCSV for something else.

Notes to Merger

⚠️ Not ready for merging