Update and add tests

[willp-bl]

• use wiremock to simulate real API calls
  • the external requests to the API are checked
  • the responses given by the mock API are in json files so they can be edited easily
• add jackson for json (de)serialisation in tests
  • this found some missing items that are in the api but not the library
  • in the future that code should be moved to main to replace current json code
• hardcode base64 test strings which will allow base64 library changes in future
• use asserts to check an exception is thrown and check messages
  • in some cases without this if the exception isn't thrown the test will still pass (the exceptions in the annotations would still be checked but this change also enables the content of the exception to be validated)
• some questions about the api/client implementation are left in the code for now
• jwt is checked on all API calls to the mocked server
• add more tests (49 -> 72)