add JumpToBottomButtom component

res/css/views/rooms/_JumpToBottomButton.scss

@@ -0,0 +1,69 @@
+/*
+Copyright 2019 New Vector Ltd
+
+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.
+*/
+
+@charset "utf-8";
+
+.mx_JumpToBottomButton {
+    z-index: 1000;
+    position: absolute;
+    // 12 because height is 50 but button is only 38 = 12+(50-38) = 24
+    bottom: 12px;
+    right: 24px;
+    width: 38px;
+    // give it a fixed height so the badge doesn't make
+    // it taller and pop upwards when visible
+    height: 50px;
+    text-align: center;
+}
+
+.mx_JumpToBottomButton_badge {
+    position: relative;
+    top: -12px;
+    border-radius: 16px;
+    font-weight: bold;
+    font-size: 12px;
+    line-height: 14px;
+    text-align: center;
+    // to be able to get it centered
+    // with text-align in parent
+    display: inline-block;
+    padding: 0 4px;
+    color: $secondary-accent-color;
+    background-color: $warning-color;
+}
+
+.mx_JumpToBottomButton_scrollDown {
+    position: relative;
+    height: 38px;
+    border-radius: 19px;
+    box-sizing: border-box;
+    background: $primary-bg-color;
+    border: 1.3px solid $roomtile-name-color;
+    cursor: pointer;
+}
+
+.mx_JumpToBottomButton_scrollDown:before {
+    content: "";
+    position: absolute;
+    top: 0;
+    bottom: 0;
+    left: 0;
+    right: 0;
+    mask: url('$(res)/img/icon-jump-to-bottom.svg');
+    mask-repeat: no-repeat;
+    mask-position: 9px 14px;
+    background: $roomtile-name-color;
+}