Added topline component and fixed string interpolation

client/src/components/ui/Topline.js

@@ -0,0 +1,19 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+
+import './Topline.css';
+
+const Topline = props => (
+    <div className={`alert alert-${props.type} topline`}>
+        <div className="container">
+            {props.children}
+        </div>
+    </div>
+);
+
+Topline.propTypes = {
+    children: PropTypes.node.isRequired,
+    type: PropTypes.string.isRequired,
+};
+
+export default Topline;