Doc: Update Sensor Explorer example

Following changes are made to the example
    - Use of Qt Quick Controls / TableView to present the sensor
      information, reducing the example to a single QML file
    - Updated launcher main.cpp for the QML example
    - Remove separate example doc for the import subproject
    - Various fixes to example doc, add a screenshot
    - Ensure import module + qmldir are built/deployed to
      correct location

Task-number: QTBUG-32881
Task-number: QTBUG-33875
Change-Id: I0ed7c7ebc916fcad6da5e3c66d81be8f348a93e1
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Make QtSensors use Q_DECL_OVERRIDE

This patch aims to make QtSensors uses Q_DECL_OVERRIDE uniformly across
the module

Task-number: QTBUG-27392
Change-Id: I5f814f93307159175f92e29a9990587c03cce96f
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>
Merge remote-tracking branch 'origin/stable' into dev

Change-Id: Ic6de4c970ff0cb3d5d1b8b6eff4ee020ba485d99