qdoc: Changed \qmlclass to \qmltype, added \instantiates

qdoc: Changed \qmlclass to \qmltype, added \instantiates

The \qmlclass qdoc command is now deprecated. Use \qmltype instead.
\qmlclass had two arguments, the QML type name and, if the QML type
was elemental, the name of the C++ class that the QML element
instantiates. The \qmltype command has only one argument, the QML type
name.

If the QML type is elemental, then the \qmltype command should be
followed by a \instantiates context command in the same qdoc
comment. e.g.:

\qmltype Item
\instantiates QDeclarativeItem

When the developer does not include the \instantiates command for an
elemental QML type, qdoc will no longer be able to detect that the C++
class name is missing, and qdoc will no longer be able to detect when
the name specified for a \qmlproperty of the elemental QML type has
the wrong name.

Task nr: QTBUG-26648

Change-Id: Ia60872a35113a6f615bfc751ce1e9db6279dfb8e
Reviewed-by: Casper van Donderen <casper.vandonderen@nokia.com>