Barometer calibration

[kylecorry31]

• [ ] Set offset directly
• [ ] Set offset via current pressure
• [x] Create CalibratedBarometer wrapper

When the user is setting this, display sea level pressure, current pressure, and the elevation used for sea level calibration so they can choose the correct offset.

[leavenode]

It will be good to get this working. I can calibrate the barometer on my Casio ProTreks(I typically use my local METAR as reference) but the readings on my various phones are still all over the place.

[kylecorry31]

@leavenode I will plan to get this done after the Photo Maps feature is release in around a month

For the most part, Trail Sense does not need it perfectly calibrated to predict weather - most of the weather prediction works on the change in pressure rather than the absolute pressure. That's why this issue was a lower priority. The only part that uses the absolute pressure is the "later" weather prediction - and that does not require it to be accurate either (within 10-15 hPa of actual should be fine). It's also a similar case with the altimeter (which already supports calibration) - that just uses changes in pressure from the reference pressure/elevation, so an accurate absolute pressure is not a strong requirement.