Add Qt Quick to feature overview and fix multimedia links
Add Qt Quick to feature overview and fix multimedia links

We need to mention Qt Quick as a key feature in the platform
overviews. I've also added links to the multimedia feature so
you can get to either the module docs (the link was wrong previously)
or the overview.

Change-Id: Ie3386da6143119f04a49f0a83cef4c3b0a31e7ac
Reviewed-by: Paul Olav Tvete <97541fb6312d77f06e19078c7c70b2c1f75fb828@digia.com>
Reviewed-by: Martin Smith <a8cc6484db2755056ccf1c457da8ca771f895dea@digia.com>

kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc