Moved declarative-camera example in the right directory.

This example was in the multimediawidgets directory but doesn't depend on
or use the QtMultimediaWidgets module. Moved to 'examples/multimedia'
instead.

Change-Id: Ic2fcc6576e95664e0002531ee378a4366daa56c1
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>