-applied a three column style
-examples categorized with Qt Creator tutorials more prominent
-added information about where to find the examples

Task-number: QTBUG-33597
Change-Id: Ia23089aec8aa453890a80bbcf03e117e0fd3c955
Reviewed-by: Martin Smith <martin.smith@digia.com>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>