Add UI for hold functionality

src/components/views/context_menus/CallContextMenu.tsx

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+/*
+Copyright 2020 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.
+*/
+
+import React from 'react';
+import PropTypes from 'prop-types';
+import { _t } from '../../../languageHandler';
+import { ContextMenu, IProps as IContextMenuProps, MenuItem } from '../../structures/ContextMenu';
+import { MatrixCall } from 'matrix-js-sdk/src/webrtc/call';
+
+interface IProps extends IContextMenuProps {
+    call: MatrixCall;
+}
+
+export default class CallContextMenu extends React.Component<IProps> {
+    static propTypes = {
+        // js-sdk User object. Not required because it might not exist.
+        user: PropTypes.object,
+    };
+
+    constructor(props) {
+        super(props);
+    }
+
+    onHoldUnholdClick = () => {
+        this.props.call.setRemoteOnHold(!this.props.call.isRemoteOnHold());
+        this.props.onFinished();
+    }
+
+    render() {
+        const holdUnholdCaption = this.props.call.isRemoteOnHold() ? _t("Resume") : _t("Hold");
+
+        return <ContextMenu {...this.props}>
+            <MenuItem className="mx_CallContextMenu_item" onClick={this.onHoldUnholdClick}>
+                {holdUnholdCaption}
+            </MenuItem>
+        </ContextMenu>;
+    }
+}