Add message bar

src/components/MessageBar.jsx

@@ -0,0 +1,15 @@
+import React from 'react';
+import { Snackbar } from "@material-ui/core";
+import { useUserContext }  from './Contexts/UserContext';
+
+export const MessageBar = () => {
+  const { error, setError } = useUserContext();
+  const open = (error !== null);
+
+  return (<Snackbar
+    open={open}
+    message={error}
+    anchorOrigin={{ vertical: "top", horizontal: "center" }}
+    autoHideDuration={10000}
+    onClose={() => setError(null)}/>)
+}