Add the HeartbeatTimer class to track a single heartbeat for a single link.
For every new received heartbeat an instance of the class is created.
Every instance emits a signal if it timed out or the timer is restarted.
Each vehicle then decides based on all different signals which link is the
priority link.

Each link updates the active property based on incoming bytes.
The vehicle tracks the active property of each link and in case of an inactive priority link it updates the priority link.

This setting enables/disables the LinkIndicator toolbar in which the primary link can be chosen.

The LinkIndicator shows the connected links and lets the user select the priority link,

Automated preflight checklists

Implement GeoFence persistence

Ignore old version 1

Automated preflight checklist: Initial commit. Note that this requires an autopilot firmware that writes the respective health flags in the SYS_STATUS mavlink message

Fix altitude change signalling

Vehicle. Expose sensor status to Qml

Simplify README with links to devguide

ArduPilot: Start possible Solo video

modify android build repo

Don't query terrain from Fly View mission items

Terrain batch fix, transect style generation fix

Not all batches would be queried

Add missing final

Fix video popup on windows

Remove debug logging

README: Add unit tests information

Refly and camera shot count support