land_detector: Hotfix to prevent ground contact detection when descending velocity is very slow with manual stick all the way down
Now the stick down check is only done in manual control and the thrust low is again mandatory to detect ground in any case.

We will be adding another parameter to set min starting temp, so this name needs to be made less generic.
Fixes typographical errors in the description

From their registers it's not possible to differentiate MS5611 from
MS5607. Here we use a little heuristic that people won't likely be
flying (or starting to fly) on very high altitude, greater than 5300m.
Even on these altitudes the error would be much lower using the MS5611
calculations for MS5607 than it is on MSL.

 - _voted_sensors_update.baro_pressure() is already in pascals

   See https://groups.yahoo.com/neo/groups/nuttx/conversations/topics/14362

to be consistent with the rest of the system

Fix typographical error