Add more unit tests to mligo

[mdales]

Adds more contract unit testing, in particular more negative testing, and also have the tests check the state of the contract. Specifically:

• Rewrite Makefile - this now supports running more complex tests, and supports platforms where you need to use docker to run the ligo tooling.
• Add more unit tests for the fa2 and custodian files
• Fixes a small bug in the fa2 contract where it returned the wrong error code
• Whitespace fixes in FA2 contract and the old "story flow" unit tests.

This is far from complete, but I think this is enough to be merged as is with the intent that we'll expand on it as we improve on things over time. It certainly is better than where we were.

[mdales]

@avsm pointed out that it might be nice to tidy away all the match testing on optionals. I did look into this (and thanks to @patricoferris for his ML support), but unfortunately in Ligo's flavour of ML I can't express a polymorphic function that contains a value comparison test, so I plan to leave them as is.

https://gitlab.com/ligolang/ligo/-/blob/dev/gitlab-pages/docs/faq/polymorphic-comparison.md