Changed the overlay's "Save" button label to "Done"

As it never actually saved anything, at least not to the database.
Whereas "Done", suggests that the editor is done with editing the current content panel.

Author: leekelleher

src/Our.Umbraco.DocTypeGridEditor/Web/UI/App_Plugins/DocTypeGridEditor/Js/doctypegrideditor.controllers.js

@@ -53,7 +53,7 @@
             $scope.overlay = {};
             $scope.overlay.show = true;
             $scope.overlay.title = overlayTitle;
-            $scope.overlay.submitButtonLabelKey = "buttons_save";
+            $scope.overlay.submitButtonLabelKey = "bulk_done";
             $scope.overlay.view =
                 umbRequestHelper.convertVirtualToAbsolutePath(
                     "~/App_Plugins/DocTypeGridEditor/Views/doctypegrideditor.dialog.html");