This is another step to isolate time from the system.

This is a step towards isolating time from the system.

 - px4_add_module now requires MAIN
 - px4_add_library doesn't automatically link

use c++ so that raw string literals can be used

to keep the behavior the same, remove the -e flags from all pwm commands
that use it in the scripts.

   Prior to onshot being added to the system. The -r of the
   "rate" command would not invoke the ioctl PWM_SERVO_SET_UPDATE_RATE
   when -r was not provided on the command line. This may have been a
   feature or a bug.

   When onshot was added to the pwm command a bug was intorduced
   that precluded the ioctl PWM_SERVO_SET_UPDATE_RATE from being
   called on -r 0.

   This commit fixes that issue, and preserves the "prio to oneshot"
   behavior of the "rate" command when -r is not specified.

  At at a period greater than the the max Oneshot pulse width
  Trigger all timer's channels in Oneshot mode to fire the
  oneshots with updated values.

cleanup and remove unused (new) params

change fmu to task

increase fmu_servo task priority to max and enable true oneshot

use lowest FMU priority which minimizes jitter

constrain oneshot updates to control group 0 events