Doc: Move Qt Quick 1 demos and their documentation

When installing the examples, we currently end up with a
QT_INSTALL_EXAMPLES/demos directory with nothing but documentation
files.

This change moves the docs and also the demos themselves into
examples/declarative/demos.

Also fixes the links in demo .qdoc files.

Task-number: QTBUG-31722
Change-Id: Ied15526be1db8437e14be786ea69eae98af8dd3f
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>