Unify system feedback templates

Also, a SystemFeedback model no longer has a `type`, it has an `intent`. This is
because SystemFeedback views have `type`, as well, and this prevents a naming
collision.

cms/static/js/models/feedback.js

@@ -1,6 +1,6 @@
 CMS.Models.SystemFeedback = Backbone.Model.extend({
     defaults: {
-        "type": null,  // "warning", "confirmation", "error", "announcement", "step-required", etc
+        "intent": null,  // "warning", "confirmation", "error", "announcement", "step-required", etc
         "title": "",
         "message": ""
         /* could also have an "actions" hash: here is an example demonstrating
@@ -32,18 +32,18 @@ CMS.Models.SystemFeedback = Backbone.Model.extend({
 
 CMS.Models.WarningMessage = CMS.Models.SystemFeedback.extend({
     defaults: $.extend({}, CMS.Models.SystemFeedback.prototype.defaults, {
-        "type": "warning"
+        "intent": "warning"
     })
 });
 
 CMS.Models.ErrorMessage = CMS.Models.SystemFeedback.extend({
     defaults: $.extend({}, CMS.Models.SystemFeedback.prototype.defaults, {
-        "type": "error"
+        "intent": "error"
     })
 });
 
 CMS.Models.ConfirmationMessage = CMS.Models.SystemFeedback.extend({
     defaults: $.extend({}, CMS.Models.SystemFeedback.prototype.defaults, {
-        "type": "confirmation"
+        "intent": "confirmation"
     })
 });

cms/static/js/models/section.js

@@ -23,7 +23,7 @@ CMS.Models.Section = Backbone.Model.extend({
     showNotification: function() {
         if(!this.msg) {
             this.msg = new CMS.Models.SystemFeedback({
-                type: "saving",
+                intent: "saving",
                 title: gettext("Saving…")
             });
         }