Add unit tests around Storm objects

[ryanbourneuk]

Expected Behaviour

All Storm objects (objects that are generated from a Storm bundle) should have full unit test coverage.

Current Behaviour

Only some Storm objects have unit test coverage.

Possible Solution

• Add #warnings around Storm objects & parsing to direct where tests should be added.
• Migrate unit tests from an old stale Obj-c branch.
• Add new tests to clear #warnings

Steps to Reproduce (for bugs)

Context

As part of the codable-refactor project, all Storm objects will be migrated from using manual JSON parsing / initialisation to using Codable. However, as ThunderCloud is used in many many apps, it'd be great for it to not break. If we determine the current state of ThunderCloud to be as expected, we can write a test suite against it - and then migrate objects to use Codable. The tests will then inform us if we have deviated from the expected behaviour.