Change templates for Quick file wizards

A Item is more light weight than a Rectangle and using it against a white
background is useless. Actually Rectangle is not very much used so Item
is a better default. Width and height are dangerous too because people
exchange them with bindings instead of using anchors or layouts.

Change-Id: I4a89ddfc0f96fb3cdb0a9ccad7fcf80b8f28b479
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>

share/qtcreator/templates/wizards/files/qtquick1/file.qml

@@ -1,6 +1,5 @@
 import QtQuick 1.1
 
-Rectangle {
+Item {
-    width: 100
+
-    height: 62
 }

share/qtcreator/templates/wizards/files/qtquick2/file.qml

@@ -1,6 +1,5 @@
 import QtQuick 2.0
 
-Rectangle {
+Item {
-    width: 100
+
-    height: 62
 }