Several updates for PX4

[bkueng]

This script is awesome!

I made the following updates:

• Added an option to use the Fuel telemetry data. This is calculated by the vehicle and might be more accurate.
• check rxpercent if it's above 99.9%
• fix labels for heading
• shorten the PX4 flight modes to avoid overlap with the heading

This should be tested with APM as well before merging.

There's a relevant PR in PX4: https://github.com/PX4/Firmware/pull/7708. This makes it fully compatible with PX4.

[ilihack]

Thank you @bkueng