[IMP] web_editor: add image filename at the end of URLs

When an image is added thanks to the media dialog, the URL that is used
was '/web/image/<id-of-the-attachment>'. Now the name of the image will
be added for SEO purposes ('/web/image/<id-of-the-attachment>/<name>').

Also protect URLs with quotes to allow spaces.

addons/web_editor/static/src/js/editor/snippets.options.js

@@ -833,7 +833,7 @@ registry.background = SnippetOption.extend({
      */
     background: function (previewMode, value, $li) {
         if (value && value.length) {
-            this.$target.css('background-image', 'url(' + value + ')');
+            this.$target.css('background-image', 'url(\'' + value + '\')');
             this.$target.addClass('oe_img_bg');
         } else {
             this.$target.css('background-image', '');

addons/web_editor/static/src/js/widgets/widgets.js

@@ -306,7 +306,7 @@ var ImageDialog = Widget.extend({
             return (r.url || r.id);
         });
         _.each(this.records, function (record) {
-            record.src = record.url || '/web/image/' + record.id;
+            record.src = record.url || _.str.sprintf('/web/image/%s/%s', record.id, record.name); // Name is added for SEO purposes
             record.is_document = !(/gif|jpe|jpg|png/.test(record.mimetype));
         });
         this.display_attachments();