Implement dialog for resending local echo transactions

res/css/views/toasts/_NonUrgentEchoFailureToast.scss

@@ -0,0 +1,37 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+.mx_NonUrgentEchoFailureToast {
+    .mx_NonUrgentEchoFailureToast_icon {
+        display: inline-block;
+        width: $font-18px;
+        height: $font-18px;
+        mask-position: center;
+        mask-size: contain;
+        mask-repeat: no-repeat;
+        background-color: #fff; // we know that non-urgent toasts are always styled the same
+        mask-image: url('$(res)/img/element-icons/cloud-off.svg');
+        margin-right: 8px;
+    }
+
+    span { // includes the i18n block
+        vertical-align: middle;
+    }
+
+    .mx_AccessibleButton {
+        padding: 0;
+    }
+}