An airframe change keeps all RC params except the flight modes. This fixes
that.

 - this is needed for the unit tests

 - add preflight_check helper

 - this flag often results in hiding useful information, or adding
   useless information to the mavlink console

 - only call prearm if preflight passes
 - prearm always provide feedback

 -  fixes #9155

Battery warning gets only fired if a battery is inserted.

The goal is to improve the readability for expressions like:
if (hrt_elapsed_time(&start_time) > 8000000)

Available since C++11

- ecl in PX4/Firmware (163fdded13d1cb48ea4849a4596feaa7025cb796): https://github.com/PX4/ecl/commit/ba2b9dfdd96d50d697165407b88b5bc94cdef84c
    - ecl current upstream: https://github.com/PX4/ecl/commit/02e319431b948f660f8548707849489d6c822fad
    - Changes: https://github.com/PX4/ecl/compare/ba2b9dfdd96d50d697165407b88b5bc94cdef84c...02e319431b948f660f8548707849489d6c822fad

02e3194 2018-04-11 Daniel Agar - cmake remove embedded vim settings
91b5bfe 2018-04-11 Daniel Agar - attitude_fw remove unused perf include
02055ac 2018-04-09 Paul Riseborough - EKF: Fix non GPS aiding data reset logic (#418)