GpsInfo: added advanced setting to display HDOP instead of FIX

We depend on HDOP as measure of GPS reliability. GPS will report 'GPS 3D Lock' with as few as 4 satellites and an HDOP of 10+. We don't depend on GPS if HDOP values are > 2 where we fly.

Added an advanced option to replace '3D Fix/No Fix' w/ numeric HDOP value in satellite info panel.