#86 OSD tweaks

[Anonymous]

Originally created by: Andrius.... (code.google.com)@gmail.com

(Enhancement)
Some OSD issues (from practical use):
- "Only show GPS coords when low and slow" - should also trigger from bad RSSI, if enabled (not only altitude/speed, but if RSSI < 30% for example)
- refresh speed on some elements is way too high. Current refresh rate is fine for AHI and (maybe) for distance/altitude. Other elements (speed, ADC inputs) change a lot and sometimes are hard to read. Suggested fix:
   * keep AHI at current refresh rate
   * average ADC inputs over 1.5 seconds and redraw them only after calculation is done (readable data)
   * average speed over 1-1.5 second and only then redraw on screen
- add support for wind direction arrow (like minimosd does - take from Remzibi branch?)