Standardize SI-Unit Calculations and InfluxDB Storage

All values (distance, speed, angles, etc.) should be calculated and stored in SI units (m, s, m/s, rad) in the backend and InfluxDB. This seemingly excludes lat/long though.

Taken from the SignalK Spec:

The values are always SI units, and always the same units for the same key. Therefore, speedOverGround is always meters per second, never knots, km/hr, or miles/hr.

See here for more info on fields and units.

The frontend should only convert for display (e.g., user preference: kn, km/h).

Tasks

• Audit and adapt backend calculations for non-SI units where applicable.