Doc: Changed \qmlclass to \qmltype and added \instantiates.

-To simplify QDoc, \qmlclass is now \qmltype.
-'\instantiates <C+++ class>' is for the types that are defined in C++.

Change-Id: I29242d33daf7b972d8b86a356b9689638866b950
Reviewed-by: Laszlo Papp <lpapp@kde.org>
Reviewed-by: Bea Lam <bea.lam@nokia.com>
Reviewed-by: Martin Smith <martin.smith@nokia.com>