Joystick: support advanced axis configuration options

[ES-Alexander]

QGroundControl reference docs

Of particular note are:

• [ ] deadbands/deadzones (including calibration)
• [ ] circle correction
• [ ] exponential scaling

[ES-Alexander]

Could maybe add tabs to the "advanced configuration" section suggested in #617, whereby the functions mapping table can be one tab, and axis configuration can be a separate one :-)

[ES-Alexander]

+1 in this forum comment