Opening/seeking/closing the file for each data chunk was extremely
expensive and drastically slowed the download process as the position
in the file increased. Over USB with large files this change + nuttx
update results in ~ 10x speedup for log downloads.

added single point to decide if we need quadchute, let the reason be passed from the source where we know what's going on

issue (GCC 6.1.1):
../src/modules/fw_pos_control_l1/fw_pos_control_l1_main.cpp:1284:27: error: implicit conversion from ‘float’ to ‘double’ to match other operand of binary expression [-Werror=double-promotion]
  if ((fabs(air_gnd_angle) > M_PI) || (ground_speed_2d.length() < 3.0f)) {

Report terrain altitude

If the circuit breaker to disable IO safety is engaged, the safety
button should still blink in the appropriate pattern: double flash for
safety off, solid on for armed.

Since the FRAM and the baro are on the same bus on the Pixracer, we
currently need to lock down everything (instead of just this SPI bus)
for the time when the params are written.
Therefore, we need to keep this locking as short as possible.

This change makes the locking even shorter by moving all param_get and
param_name and param_size calls out of the lock.

Previously, the accel DLPF was not set, so it's not clear what the
settings are or should be.

This is a big refactor and general cleanup of the land detector. The
main functional change is to share the hysteresis lib across all land
detectors.