[rotorcraft] v_adapt: limit min/max estimated hover throttle

The adaptive vertical filter estimates the ratio of vertical acceleration over thrust command.
In effect this will now limit the throttle applied in hover between 20% and 75% of max throttle by default.
[rotorcraft] v_adapt: reset while not in_flight
[rotorcraft] v_adapt: config improvements and refactor

- GUIDANCE_V_ADAPT_INITIAL_HOVER_THROTTLE settable in % with default of 0.3
- GUIDANCE_V_ADAPT_THROTTLE_ENABLED:
  - TRUE by default if GUIDANCE_V_NOMINAL_HOVER_THROTTLE was not defined
  - FALSE by default if only GUIDANCE_V_NOMINAL_HOVER_THROTTLE was set in airframe file
    (for backwards compatibily)
- switching between nominal_trottle and the adaptive estimate during operation via settings
[conf] update some airframe examples to GUIDANCE_V_ADAPT changes
[rotorcraft] v_adapt: include generated airframe.h
Merge pull request #495 from flixr/v_adapt_limits

adaptive thrust estimation limits

- GUIDANCE_V_ADAPT_INITIAL_HOVER_THROTTLE settable in % with default of 0.3
- GUIDANCE_V_ADAPT_THROTTLE_ENABLED:
  TRUE by default if GUIDANCE_V_NOMINAL_HOVER_THROTTLE was not defined
  FALSE by default if only GUIDANCE_V_NOMINAL_HOVER_THROTTLE was set in airframe file (for backwards compatibility)
- switching between nominal_throttle and the adaptive estimate during operation via settings