Publish mauth-test-utils

[colinphill-mdsol]

After running into some maintenance issues with clojure-mauth-client, I would like to write a new version that reuses the production-proven Java core here, including the testing utilities. I first looked at adding it as a module here, with @tmilner's help, but we were not able to find a usable Clojure plugin for sbt.

This change simply publishes the mauth-test-utils module as an artifact, so that other JVM-based projects with different build tools can reuse it.

Other alternatives considered:

• Write the Clojure implementation without using mauth-test-utils. This would involve reinventing an excessive number of wheels.
• Migrate this project to gradle or maven, which are generally able to support any JVM language. This may be worth considering in the long term, but it would be a major undertaking.
• Add a second build process within this project, living alongside sbt. This would probably be unreasonably complex and confusing.