Logging: create a new module for logging data

This uses Streamfs to write the logs using PIOS_COM
to a circular buffer on the flash chip. It starts
writing as soon as the system is powered up.
Logging: add code to download log files while running

This is mirrored from the picoC code and allows downloading
from log files in 32 byte chunks.
GCS/Logging: code to download logs from running FC

This adds a menu option that will iterate through a log
file and download it from the flight controller to a
file.