- I enabled it by default mostly for testing purposes
- Disabling it reduces resource usage as most setups don't need it

This is a step towards isolating time from the system.

Keeps things more modular.

The threads running commands for clients through the Posix daemon used
to write to a char buffer through snprintf (etc.) which was then written
directly to the file descriptor, whereas in the other case printf
(etc.) was used to write to stdout (FILE*). Both versions used some
macro's and repeated code to have the same output.

This change unifies these two cases by using a FILE* in both cases. The
(line) buffering is done by the standard C library's implementation
(just like with stdout), and px4_log.c now uses the same code in all
cases (using fprintf, etc.) for printing (colored) output.

- move the update after the integration: a new computed jerk has an impact at the next epoch only
- add jerk reduction in case of too large integration time: when a jerk of "min_jerk" during dt is too much
- add jerk reduction if the integration time is larger than the predicted one and that integrating that jerk would lead to an acceleration overshoot
- rename some variables

- fsync can be a long blocking operation, so we need to make sure the main
  logger thread does not block during this time, when it tries to aquire
  the mutex
- fixes calling fsync on an invalid file descriptor

To get it field-tested. This can be reverted for a release...

- mission logs are stored in a separate directory mission_log
- It's disabled by default
- Does not increase RAM usage if disabled (if enabled, only 300 bytes)
- Log rotate does not apply to the mission logs

Some message formats are longer than the 300 bytes. We can split the writes
because we have to wait until they are written anyway.

256 subscriptions are enough for now.
Reduces RAM usage by 300 bytes.

Not used yet, it should not affect anything, except for slight RAM
increase.

Previously the formats of all known uorb messages were written.

- reduces header size by about 13KB
- reduce ulog_message_format_s size to reduce required stack size.
  Largest message format is about 1000 bytes.

Make sure vehicle_air_data & vehicle_magnetometer are logged if ekf2 replay
is disabled.

- fixes #10345

This data is published at the GPS publication rate and only when on ground.