Add Keyboard shortcuts dialog

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

res/css/_components.scss

@@ -65,6 +65,7 @@
 @import "./views/dialogs/_GroupAddressPicker.scss";
 @import "./views/dialogs/_IncomingSasDialog.scss";
 @import "./views/dialogs/_InviteDialog.scss";
+@import "./views/dialogs/_KeyboardShortcutsDialog.scss";
 @import "./views/dialogs/_MessageEditHistoryDialog.scss";
 @import "./views/dialogs/_NewSessionReviewDialog.scss";
 @import "./views/dialogs/_RoomSettingsDialog.scss";

res/css/views/dialogs/_KeyboardShortcutsDialog.scss

@@ -0,0 +1,65 @@
+/*
+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_KeyboardShortcutsDialog {
+    display: flex;
+    flex-wrap: wrap;
+    -webkit-box-orient: vertical;
+    -webkit-box-direction: normal;
+    flex-direction: column;
+    margin-bottom: -50px;
+    max-height: 700px; // XXX: this may need adjusting when adding new shortcuts
+
+    .mx_KeyboardShortcutsDialog_category {
+        width: 33.3333%; // 3 columns
+        margin: 0 0 40px;
+
+        & > div {
+            padding-left: 5px;
+        }
+    }
+
+    h3 {
+        margin: 0 0 10px;
+    }
+
+    h5 {
+        margin: 15px 0 5px;
+        font-weight: normal;
+    }
+
+    kbd {
+        padding: 5px;
+        border-radius: 4px;
+        background: $roomheader-addroom-bg-color;
+        margin-right: 5px;
+        min-width: 20px;
+        text-align: center;
+        display: inline-block;
+        border: 1px solid black;
+        box-shadow: 0 2px black;
+        margin-bottom: 4px;
+        text-transform: capitalize;
+
+        & + kbd {
+            margin-left: 5px;
+        }
+    }
+
+    .mx_KeyboardShortcutsDialog_inline div {
+        display: inline;
+    }
+}