supports EEPROM handling and t5x configurator

first version that supports t5x configurator. no need to recompile the
binary to do changes.
doing that way we gained more than 500bytes free RAM, while the ROM is
still below 15k.
also fixed: throttle trigger threshold for flight timer is now tied to
the throttle output rather than A2 input. setup mode now always turns
off buzzer and uses LED instead. LED is used to signal apply action and
save action from the configuration software.