Rename namespace QtMultimedia -> QMultimedia

Rename namespace QtMultimedia -> QMultimedia

Main code, examples, tests and docs updated. Method:
1. Mass find+replace "QtMultimedia::" -> "QMultimedia::"
2. Hand-modified declaration in qtmedianamespace.h/cpp

For consistency (with minimal disruption), namespaces with a "Qt" prefix
will be renamed.

Part of the Header Consistency Project
(http://lists.qt-project.org/pipermail/development/2012-October/007570.html)

Change-Id: I1fbc43a1aa91d996aa61869fcd8d05186bf7cf6d
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>