Compass isn't supported

The current back-end being used for QtSensors doesn't support the compass sensor found in most modern phones (including krillin and mako). Compass readings are useful for augmented reality, navigation, geocaching and astronomy/sky viewer applications.

Steps to reproduce:

1) Run following QML:

import QtSensors 5.0
import Ubuntu.Components 1.1

MainView {
        Compass {
            active: true
            onReadingChanged: {
                console.log("Reading: " + reading.azimuth);
            }
        }
}

Expected result:

 Compass readings should be output on the console

Actual result:

 No output.