Move thanks API into main commons codebase

[psh]

Very quick refactor -

• Moved the "thanks" API call (last step of a review) into the main code-base, out of the data client
• Converted the API interface and the response class to kotlin
• Setup injection to pass the ThanksInterface into the ThanksClient instead of the large Service interface from the data-client

In the process, I updated the unit test (swapping from Service to ThanksInterface) but otherwise keeping the functionality intact. Tested in the running app and all seems to be fine.

This relates to the discussion in #5165

[nicolas-raoul]

Just tested, it works great, thanks a lot! :-)