Graceful period between disarm and BB stop recording

[gongtao0607]

I always disarm my Heli right before crashing. It will then lose a second of important BB data at crashing. I think we should add a few seconds of graceful period between disarm and stopping the recording. 2 seconds should be enough for most cases.

I know I can use "Switch" logging mode and customize it in the radio to keep it record, or use throttle hold instead of disarm, but I still feel this is a sweet small feature to have.