[frontend] Use new GET custom_emoji admin api (#908)

* use new GET custom_emoji admin api

* use url instead of static_url, add link to emoji admin api tracking issue

* fetch all local emoji

web/source/settings/components/back-button.jsx

@@ -0,0 +1,30 @@
+/*
+	GoToSocial
+	Copyright (C) 2021-2022 GoToSocial Authors admin@gotosocial.org
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU Affero General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU Affero General Public License for more details.
+
+	You should have received a copy of the GNU Affero General Public License
+	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+"use strict";
+
+const React = require("react");
+const { Link } = require("wouter");
+
+module.exports = function BackButton({to}) {
+	return (
+		<Link to={to}>
+			<a className="button">&lt; back</a>
+		</Link>
+	);
+};