* CMake: Set warning level and disable -Waddress-of-packet-member

Mavlink fails terribly on the check for -Waddress-of-packet-member
but this is not a problem of QGC, if I don't remove this warning
it's impossible to look at the terminal for QGC warnings.
This needs to be fixed however, but this is not the place.

Video is still not being displayed, for some reason

qextserial library is no longer maintained, suggest we move
to this library, also greater chance for thread safety,
library now builds in cmake, will add Serial2 sources to
handle the new qserial, should easily plug into serial interface
now.