Rename Qt Quick-specific classes to QQuick*

The QSG (SceneGraph) prefix is too generic for
Qt Quick(2)-specific classes.

All the classes and files in the declarative/items
directory have been renamed.

In particular, for classes that are currently public,
the renaming is as follows:

QSGView --> QQuickView
QSGCanvas --> QQuickCanvas
QSGItem --> QQuickItem
QSGPaintedItem --> QQuickPaintedItem

The header files have been renamed accordingly
(e.g. qsgview.h --> qquickview.h).

Change-Id: Iac937fff81db20bb639486a793c3aeb5230b038c
Reviewed-by: Kent Hansen <kent.hansen@nokia.com>