SE(3): only pass valid GPS data

Previously whenever GPS data was available, it was
passed to the underlying architectures. Now our standard
GPS thresholds are applied first.
SE(3): only pass valid GPS data
SE(3): store the NED position

This only stores the conversion for good GPS
update values.
SE(3): update the NEDPosition properly

This was storing the data before it was computed.
SE(3): do not allow updates with bad positions

Previously getNED did not verify that the home location was
set before performing an update.
CFNav: new filter stubs

This will be based on the our complementary filter and the
arducopter navigation complementary filter.
CFNav: port basics of algorithm from arducopter

This is a simple complementary filter fusing the accels and
the position. It currently does not have the latency terms
for GPS and Baro, not is it using the NED rotated sensor
data.
CFNav: update the predicted state

Using the accels rotated into the NED frame. Also pass the
data from the internal data to the fetch method.
CFNav: compute the position error based on lagged state

The GPS has a latency of approximately 400 ms so update the
position error by comparing the latest GPS update compared
to a state estimate that old.
CFNav: fill the history when initializing

Make sure the history is filled with valid data when initializing.
This still does not cover the case when the GPS is not updated for
a while.
CFNav: add settings to UAVO

This lets us adjust the navigation filter settings without
recompiling.
CFNav: the history is meant to be position_base

I was using position which already has the applied
correction.
CFNav: zero all internal variables at powerup
CFNav: fix some constants
CFNav: store the NED accel after rotating it
VtolPath: remove NED accel calculation

This should be handled by the state estimation.
CFNav: store the internal data to a UAVO
CFNav: store NEDAccel with the correction from filter
Filter: make sure to calculate correct dt

Previously had hardcoded dt which was obviously
incorrect.
Fix: forgot cfnavstate