Qbs: Small header cleanup

Change-Id: Ie8972395d7a0f2af18810954c3d8311357afd1cb
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Qbs: Use proper mimetype for qbs project files

Change-Id: I88cc3b74bff44d11b019868dc40d43788c035558
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Squish: Added test for QTCREATORBUG-3620

Task-number: QTCREATORBUG-3620

Change-Id: Ibfcc1a51825b019fd834644da0344143725b0b70
Reviewed-by: Christian Stenger <christian.stenger@digia.com>