Doc: Adding Qt Multimedia Widgets documentation.

-added landing page and module page
-linked to Qt Multimedia and Qt Widgets
-excluded multimediawidgets dir from the Qt Multimedia documentation

Task-number: QTBUG-29339
Change-Id: Iaa8dc4117505d5635b8cab97ed5c10e9c4a289e6
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Sze Howe Koh <szehowe.koh@gmail.com>

src/multimedia/doc/qtmultimedia.qdocconf

@@ -29,7 +29,7 @@ qhp.qtmultimedia.subprojects.qmltypes.indexTitle = Qt Multimedia QML Types
 qhp.qtmultimedia.subprojects.qmltypes.selectors = fake:qmlclass
 qhp.qtmultimedia.subprojects.qmltypes.sortPages = true
 
-exampledirs += ../../../examples \
+exampledirs += ../../../examples/multimedia \
                snippets
 
 headerdirs += ../..
@@ -38,6 +38,6 @@ imagedirs += src/images \
 
 sourcedirs += ../..
 
-excludedirs +=
+excludedirs += ../../multimediawidgets
 
-depends                 += qtcore qtdoc qtquick qtqml
+depends                 += qtcore qtdoc qtquick qtqml qtmultimediawidgets

src/multimedia/doc/src/qtmultimedia-index.qdoc

@@ -32,6 +32,8 @@
 
     Qt Multimedia is an essential module that provides a rich set of QML types and C++ classes to handle multimedia content. It also provides necessary APIs to access the camera and radio functionality.
 
+    The \l{Qt Multimedia Widgets} module provides widget based multimedia classes.
+
    \section1 Getting started
 
     The QML types can be imported into your applciation using the following import statement in your \c {.qml} file.