IdleScreen: fix coverity ID 746880 Uninitialized pointer field

Remove m_upcomingList that Coverity is saying is uninitialised it's currently
unused.
PlaybackBox: fix coverity ID 1023904 Uninitialized pointer field

In PlaybackBox::PlaybackBox(): Several fields are not initialized in the
constructor.
MediaRenderer: fix coverity ID 700947 Uninitialized pointer field

In MediaRenderer::MediaRenderer(): There was a couple of code paths in the ctor
where m_pUPnpCMGR could end up being uninitialized.
MHListGroup: fix coverity ID 700819 Uninitialized scalar field

In MHListGroup::MHListGroup(): Several scalar fields are not initialized
by the constructor.
MHScene: fix coverity ID 700817 Uninitialized scalar field

In MHScene::MHScene(): Several scalar fields are not initialized by the
constructor.
Merge remote-tracking branch 'upstream/master'