Warning and explanation for voltage drop.

Audio fix for PX4

fixed spelling error in toolbar battery consumed

Low pass filter on RC RSSI

Generic AERT and AETR airframe support

Pull image size from FirmwareImage object

Remove QSerialPortInfo from mobile build

This is needed for firmware upgrade which is not part of mobile

Better handling of vendor and product ids

Serial link runs on main thread

Esc cal: Yellow text for prop warnings

This is needed for Android since it needs to communicate with java apis
which require everything on the main thread. The additional thread was
not really needed since you can implement using a signal based approach
which ends up being the same thing.

Parameter validation

Major re-write of Firmware Upgrade

Usability plus, new features:
- 3DR Radio support
- APM Stack support

Moving to Dev 2.6

Switch to 2.5.2