Adjust qml scanner example to high dpi display

[ChangeLog][QtBluetooth][General] QML scanner example
has been optimized for high DPI displays. This ensures a better
user interface for Android and Blackberry devices.

Change-Id: If757cd9faddc155cbb4bb034885662abc84fc7a6
Reviewed-by: Aaron McCarthy <mccarthy.aaron@gmail.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>