PuzzleTime Sync | Final changes on PuzzleTime API

[ManuelMoeri]

After talking with HR we have found a solution to the problem of persons needing to exist before being saved as employed.

Modfiy the is_employed to not only select currently employed people but also people that will be employed over the span of the next three months.

TODO

• [x] Modify the PuzzleTime API as described
• [ ] Make sure everything works as expected
• [ ] Tests