-change in Qt Multimedia from "Qt Multimedia Overview" to "Multimedia".
-central point for multimedia in Qt. Title is consistent with other
topics.

Change-Id: I6cef9ff286451232ff62879f70fe189f67267e16
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Reviewed-by: Geir Vattekar <geir.vattekar@digia.com>