Add CI support for Asset Store upload

[edwardrowe]

The current asset store upload process has a lot of pain points that can ideally be automated.

Here is the process:

1. Merge everything to master after it's passed testing on staging
2. Deploy a GitHub release
3. Create a new branch off master called "asset-store-v1.x.x-unity-5.5.5" (or whatever minimum version of Unity we are supporting)
4. Open the project using Unity 5.5.5 (on Windows because this no longer works on Mac 😠)
5. Delete everything except Assets/RedBlueGames/MulliganRenamer, and the Testing folder
6. Download the Asset Store Tools package if you don't have it locally (it's ignored in gitignore)
7. Create a new draft release on the Asset Store publisher page
8. Submit Mulligan through the Asset Store Tools in Unity.

This has a lot of clear pain points. Especially opening the project in Windows on Unity 5.5.5.

The ideal CI workflow to me would be:

• Either tag or open a branch off master to indicate we need a release. I like the idea of tagging it "asset-store-v1.7.X"
• IDEALLY this would open up a draft on the asset store (lol)
• Docker Image opens up the project in the minimum unity version... I guess. We'd need to verify it works so we'd want to be running tests on this version as well.
• Delete the unused assets
• Submit the package to the backend

(This Issue is mainly to get this documented for future me 😎)