This commit implements possible switching BT on and off during a session,
so not needing a restart of the app when the user forgot to switch
it on when starting the app.
For this, the following needed to be done: 1) create a handler that
reacts on local BT device status changes. 2) repopulate the connection
list in the download screen when a BT status change is detected.
Notice the subtile change of the Q_INVOKABLE btEnabled() function
to a Q_PROPERTY. This gives a nice dynamic behaviour when
switching BT on/off with the app open.
Fixes: #556
Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>
ba4058667a