Bug 1011393 - Add support for 'csp' entries in Manifest Helper. r=fabrice

dom/apps/AppsUtils.jsm

@@ -893,5 +893,9 @@ ManifestHelper.prototype = {
 
   get role() {
     return this._manifest.role || "";
+  },
+
+  get csp() {
+    return this._manifest.csp || "";
   }
 }