Doc: Moved content from qtdoc

Doc: Moved content from qtdoc

- The qdoc pages were related to qtcore and they were
referring to snippets inside the qtcore module boundary.
- Fixed the exampledirs for QtCore to include the examples
that are referred by the \snippet instances in the
moved qdoc pages work.

Change-Id: Ibb6dbb131920ea8692a203f6145863e5012e4602
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
(cherry picked from commit 69e602941112da325b1154e0dc52714bc27a2cc8)
Reviewed-by: Sergio Ahumada <sergio.ahumada@digia.com>