Accessibility: Use factory function instead of plugin

[ChangeLog][QtQuick] Accessibility for Qt Quick is now included in the
qtquick library instead of being a separate plugin.

Change-Id: I26a7ed14b8a387662cea8f89218485be50033e34
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>
Skip nodes with no vertices when preparing batches.

Nodes with no veritces end up overlapping with everything so they
tend to lead to poor batching. In my specific case, the empty
nodes came from the QQuickTextNode, but it is a valid usecase
so better to handle it gracefully in the renderer.

Change-Id: Ic09c202a2675f806f2124cd436027afcd2654452
Reviewed-by: Michael Brasser <michael.brasser@live.com>