Split API related code to new tjf.api package
Splits classes that are directly involved in answering API requests to a
new tjf.api package.
Related MRs:
- !30 (merged)
- !31 (merged)
- !29 (merged)
- !28 (merged)
- !27 (merged)
- !26 (merged)
- !25 (merged) (This MR)
- main