New command tuneopt to handle settings for TUNE pot ("quadcopter" only)

The new command "tuneopt" will allow setting the option and values for
the tune pot (Channel 6) for ArduCopter. The Tune feature
offers a wide range of parameters that can be tuned. The list of the
parameters can be shown with the sub command "list".

Signed-off-by: Quy Tonthat <qtonthat@gmail.com>