Move the list of graphical effects to the index page

It's pointless to have the contents of http://doc.qt.io/qt-5/graphicaleffects.html on its own page when there is plenty of room under the Effects section of the landing page:

http://doc.qt.io/qt-5/qtgraphicaleffects-index.html

At least we should follow the convention of referring to the list of types as "QML Types" so it's easier to spot.