Rename variables to match paper

[philihp]

• Refactor and rename variables in the src/models/ such that they match the variables defined in the PDF. This will make the code easier to maintain and perhaps help others port to other languages.
• e.g. sigSqToCiq should probably be some variation of qEta, since it's related to η_q defined on page 287, §3.1.1
• The unit tests should protect you from making any catastrophic changes.

[mstofirova]

Hello, can I work on this?

[philihp]

Go for it :)

Please ask questions if you get stuck on anything. I would suggest a different and separate PRs for each model, and perhaps another that renames config vars to be more in line with the paper. I would prefer multiple smaller, incremental PRs.

[philihp]

"EPSILON" should be "KAPPA"