Web service endpoint to calculate reading.

Accept a reading object via POST, calculate based on available measurements (may only include declination, etc), return calculated reading.

Operations app will use this while users are entering values, and then create/update via a separate call once the user clicks save.

When, ideally, will this endpoint be called? Im thinking of two possible scenarios:

1. On any edit. The user will receive the same reading object back until at least one absolute can be defined, then more as data becomes available
2. At checkpoints. The user will only receive a new reading object back when a section of the form(declination/inclination/marks) is completed or updated(and no values were updated to be empty).

This changes the validation of these groups a bit. If we were to call this on any edit then we would need to add validation fields to Reading where full sets of measurements(mark, inclination, declination) are marked as defined or not. If at checkpoints, we would only need to pass a sub-list of measurements from the front-end and FastAPI would just need to check what measurement grouping was provided.

@jmfee @ehunter Thoughts?

mentioned in merge request !91 (merged)

closed with merge request !91 (merged)

mentioned in commit 6d204e78