non-jira: add missing video element in tinymce placeholder

src/main/webapp/static/js/tinymce4/tinymce/plugins/olatmovieviewer/css/content.css

@@ -2,6 +2,8 @@
 	border: 1px dotted #cc0000;
 	background-position: center;
 	background-repeat: no-repeat;
-	background-color: #ffffcc;
+	background-color: #ffffcc;
+	background-image: url('olatmovieviewer.png');
+	background-size: 32px 32px;
 	display: block;
-}
+}
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