Set the minimum qbs version on the project.

So people will understand why they can't open the projects with older
Creator versions.

Change-Id: Ie9291096ba001b0d31a58d834ba23c95a569d20f
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

qtcreator.qbs

 import qbs 1.0
 
 Project {
+    minimumQbsVersion: "1.3"
     property bool withAutotests: qbs.buildVariant === "debug"
     property string ide_version_major: '3'
     property string ide_version_minor: '1'