The override checking was scattered across two places and is now unified
in controls_tick(). The part in mixer_tick only decides which mixer (or
none) to use give the override flag.

This fixes a bug where multirotors got into override mode when the FMU
is dead/not responding.
The main bug was that the check was for FMU_OK || MANUAL_OVERRIDE_OK
in order to get further in the override checks.

Also a mixer_tick was called inside the controls_tick even though these
are called in px4io.c after each other anyway.

The FMU_OK flags are later checked anyway based on
system_state.fmu_data_received_time.

In order to test what happens in px4iofirmware when the FMU stops
sending PWM or control commands, I added a test mode. When the test mode
is activated, no controls are sent.

mainapp.config can't be renamed to px4.config just yet because it would
clash with the name used for the DSP side.

It currently gets cut off on mini-dm, split it into multiple lines
so all of it comes through.

Not sure why the Mode enum exists in the first place...

But the basics are working. N.B. To Stop the moros a value of 0 need to be
sent. LED color mask are misleeding - LED is On or Off per ESC.

The FMU was lacking support to do the ESC calibration. This is needed
for Pixracer.

If disarmed PWM values have been set, we can't accept a disarm command.
If we did, the PWM output stop alltogether after the high pulse of the
ESC calibration.

Once the PWM outputs are initialized, there is no point in
de-initializing them again.

This brings fixes for Edison which should not have any influence on
Snapdragon or Raspberry Pi.

* logger: prevent logpath buffer overflows

The handling of the log path had the potential to cause buffer
overflows, especially on POSIX platforms where the paths are often much
longer than just 64 chars.

* sdlog2: prevent logpath buffer overflows

When the log folder path was created, this was done with the unsafe
sprintf function instead of snprintf. This caused buffer overflows in
SITL but the overflow was usually not detected until recent testing of
some work in progress.