[sensorfw] need to run init after sensord has been restarted

This ensures things are setup and work properly.

Change-Id: I23c8b53e760d49695c5ae207eed77a2e7d2be3a4
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Series of crash fixes from Mer, squashed

        1)tracing plugin loading

        2)m_remoteSensorManager can be nullptr

        But it seems it does not solve incorrect initialization in the case
        manager interface is nullptr: init() for different sensors does not
        check initDone

        3)split initSensor() to template function and function

        most of initSensor() does not depend on template param, so it is
        better to split it -> less code should be generated

        4)do not use sensor manager if it is invalid

        5)correct class members initialization order

        6)assert sensor interface is not null

        From what I saw according to logic it should not happen so using
        Q_ASSERT for better maintainability

        7)check local interface pointer in SensorfwTapSensor::start()

        Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>

Change-Id: I5c1bf3999ad2268c0dba9b3fe511d999c2e63fd9
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Restore setting of sensors interface.

Change I5c1bf3999ad2268c0dba9b3fe511d999c2e63fd9's forward porting from Qt 5.1
removed this, thus the interface was never set, thus sensors all broke.

Change-Id: If3b14b5ebd20e6cb64bc2000b23a2c1e37d36b05
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Add missing word to QCompass documentation.

Change-Id: I46b9a3c20b5169843292057439c80c859ccc7e82
Reviewed-by: Lorn Potter <lorn.potter@jollamobile.com>
Merge remote-tracking branch 'origin/5.3' into 5.4

Conflicts:
	src/plugins/sensors/sensorfw/sensorfwproximitysensor.cpp
	src/sensors/qcompass.cpp

Change-Id: Idfcbbfe1757a4b827663453abc27f4026cd3d752