Add libudev-dev to linux build requirements

QGC depends on libudev-dev to build, include this in the list of packages to install.

Airframe config: fixed hexa copy and paste error

PX4 config: Remove the specialized throttle handling - this needs testing, but doing the math on paper it doesn’t look like a special case is needed / wanted here.

Use the reversed values for the four control channels as well. Not using them would make the display very confusing.

Enable RC calibration mode during RC calibration to tell vehicle to ignore stick inputs for that period

Added more generated files to the .gitignore.

Updated Linux build info in readme

Remember to init submodules for "qupgrade"

Even more warnings

Reorder warnings

Update to Eigen 3.2.0

add xbee library folder for linux

disable -Werror

Warnings work

TeamCity caught this, but I thought the error was from my warnings
work. Turns out it was a real build failure. Windows doesn’t know which
floating point floor to use. In reality the parentheses are in the
wrong place and should be the floor of the divide by 2. But integer
division is always floor, so it’s not needed at all.