Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Previously the first activeChanged signal got lost because it was not connected yet to the LinkInterface which resulted in a link incorrectly shown as inactive.

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.