QtIFW

Doc: update the Tutorial section

Updated according to user feedback to make descriptions clearer.
Added documentation for all sections in config.xml, explained HomeDir,
and added a link to variable list.
Deleted an obsolete note.
Updated screenshots.

Change-Id: I255569f8a09c7c3b996b6e201c5469874027cf60
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>
Reviewed-by: Niels Weber <niels.weber@theqtcompany.com>