eglfs: Move reusable functionality to eglconvenience

The cursor implementation is generic GL(ES) code that should be shared
by all the present and future egl-based embedded platform
plugins. Follow the pattern of QEGLPlatformContext and move this class
into eglconvenience as QEGLPlatformCursor.

Similarly, the common bits from the context implementation context are
moved back to EGLPlatformContext.

eglconvenience has now base classes for integration, screen, window,
etc. too. By using these, eglfs becomes much smaller and cleaner. This
also paves the way for creating new, separate EGL-based platform
plugins for Android, embedded Linux, etc.

Also added some documentation to each of the base classes.

devicediscovery is now fixed to be usable on any platform. The
implementation in this case is naturally a dummy one. This finally
allows using it from anywhere without myriads of ugly ifdefs.

Change-Id: I02946e360c04e02de7fe234a23a08320eff4ccf5
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>
qmake: cleanup DISTFILES

Do not include the project file twice or other
.pr? files outside the project tree.

Task-number: QTBUG-21910
Change-Id: I62af842282ccdc5b9099d9227d5395ebe3f0698c
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
QNX: Make window groups work reliably

Window group related code worked previously only for the 'root'
window and other windows that had no parents (which then joined
the window group of the root).

Introduced a new function joinGroup that makes the group related
calls, this can both join and leave groups.

Default group joining is performed in setVisible now rather than
setScreen.  The advantage of setVisible is that one can rely on it
getting called at some point but it is also possible to create and
interact with a QQnxWindow before it is called.  This allows
the default group handling to be overridden via the native
interface.  If the group is set (or explicitly not set) then the
default handling is not done.

joinGroup is also called from setParent so that if the parent window
is changed the window joins the parent group.

Change-Id: I03e3801ecb4e4cf901c02e45f00472a87692c2ec
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>
QNX: Avoid crashing on exit when have a cover window

QQnxScreen destructor was leaving the cover window to a reference
to it leading to a crash when the cover window itself was destroyed.

Change-Id: Id82097d54fea79b0b9ec1cef439bd704da9ca453
Reviewed-by: Kevin Krammer <kevin.krammer@kdab.com>
Reviewed-by: Bernd Weimer <bweimer@blackberry.com>
Reviewed-by: Fabian Bumberger <fbumberger@rim.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>