Show estimated user position accuracy error.
Move user position error bounds check to PositionCalculator.
Accept user provided proximity zone range.  Allow calibration reset.
Convert everything except RSSI distance estimation from meters to feet.
Fix math error.
Add scaling.
Merge master.
Merge cc-ft-to-m.
Fix scaling and accuracy.
Merge pull request #26 from ritnorthstar/cc-show-accuracy

Scaling.