Remove core business logic from controller to unbloat it

[harley-harris]

• Create generic fetch function to make API call and jsonify response
• Create service files to parse jsonified response and return desired values
• Update tsconfig to fix compilation error related to module resolution

[harley-harris]

@antoni-devlin - i did initially think about splitting up the changes related to the API, and went with that approach initially. But I found the logic to be very similar between the services and the logic is very simple. So in this case I think it's better to keep them as one commit. Also, the second API call relies on the value returned from the first call, so I think it's better to keep the changes coupled together. @huwd might have more comments?

The tsconfig change should defo be a separate commit, so I will split that out.

Thanks for the review!