Largest change is that once a link is added to LinkManager it maintains
ownership and is responsible for delete. If you need to delete a link
use LinkManager::delete. Also added guard code to assert if a Link is
deleted outside of LinkManager.

- allow unit tests to use QGCApplication
- clear global singletons for each unit test run

Centralize all connecting and disconnecting of links through
LinkManager::[Connect|Disconnect]Link api. Connect/Disconnect no longer
allowed through LinkInterface. This allows creation of new
LinkManager::setConnections[Suspended|Allowed] methods to disallow
connections as needed.

The details on the success/errors for the MAVLink protocols are now shown for each link as tooltips that are updated every 5s. Values are currently wrong and unsure why as of yet.

The details on the success/errors for the MAVLink protocols are now shown for each link as tooltips that are updated every 5s. Values are currently wrong and unsure why as of yet.

Significantly bugfixed persistence and link adding/removal. Not yet fully there, but getting closer to release

Cleaned up communication structure significantly, should now be easier to add new links. Signal bytesReceived(link, QByteArray) is now only way to pass on newly received data