GPS spike detector

[LorenzMeier]

We will need a GPS spike detector which does several things and probably can be a standalone thing like the terrain estimator. Maybe this is also something LPE already handles.

• It detects excess acceleration suggested by GPS
• It estimates the resulting velocity and position offset
• It allows to remove that offset over some time as the GPS estimate slowly recovers / comes back

[LorenzMeier]

Log with spike happening:
http://logs.uaventure.com/view/Cp3XkZ2EAvjA4W4xi4sRDk#Velocity_PLOT

[kd0aij]

@LorenzMeier It looks to me as though the velocity plot is correct. Also, I'd appreciate an answer to the question I asked in #2790 (comment); if I'm right that log exposes a bug in the altitude control logic.

[LorenzMeier]

@Tumbili Could you have a look? Is this what you fixed here? #3229

[LorenzMeier]

Will be done in EKF2.