Refactor Conjure and Minion solution checking using BTreeMap

[niklasdewally]

When checking solutions against the integration tester, I did a few hacky things with JSON string comparisons to get around the fact that HashMaps do not implement Eq, Hash, so cannot be compared, put in sets, etc.

Now we use BTreeMap instead, which does implement these, so some cleaning up is likely possible.

See also: #531