Add assets for animated dropbox teaser.

services/web/public/stylesheets/app/editor.less

@@ -411,3 +411,15 @@
 	.img-responsive;
 	margin-bottom: 5px;
 }
+
+.dropbox-teaser-video-container {
+	margin-top: -@modal-inner-padding;
+	margin-left: -@modal-inner-padding;
+	margin-right: -@modal-inner-padding;
+	margin-bottom: 5px;
+	overflow: hidden;
+}
+.dropbox-teaser-video {
+	width: 100%;
+	height: auto;
+}