message: disable "Accept"/"Decline" buttons on verif tile after clicking
  to avoid sending double events
diff: @@ -27,6 +27,7 @@ import {RIGHT_PANEL_PHASES} from "../../../stores/RightPanelStorePhases";
  export default class MKeyVerificationRequest extends React.Component {
  constructor(props) {
  super(props);
  + this.state = {};
  }
  componentDidMount() {
  @@ -58,6 +59,7 @@ export default class MKeyVerificationRequest extends React.Component {
  };
  _onAcceptClicked = async () => {
  + this.setState({acceptOrCancelClicked: true});
  const request = this.props.mxEvent.verificationRequest;
  if (request) {
  try {
  @@ -70,6 +72,7 @@ export default class MKeyVerificationRequest extends React.Component {
  };
  _onRejectClicked = async () => {
  + this.setState({acceptOrCancelClicked: true});
  const request = this.props.mxEvent.verificationRequest;
  if (request) {
  try {
  @@ -135,9 +138,10 @@ export default class MKeyVerificationRequest extends React.Component {
  subtitle = (<div className="mx_cryptoEvent_subtitle">{
  userLabelForEventRoom(request.requestingUserId, mxEvent.getRoomId())}</div>);
  if (request.requested && !request.observeOnly) {
  + const disabled = this.state.acceptOrCancelClicked;
  stateNode = (<div className="mx_cryptoEvent_buttons">
  - <FormButton kind="danger" onClick={this._onRejectClicked} label={_t("Decline")} />
  - <FormButton onClick={this._onAcceptClicked} label={_t("Accept")} />
  + <FormButton disabled={disabled} kind="danger" onClick={this._onRejectClicked} label={_t("Decline")} />
  + <FormButton disabled={disabled} onClick={this._onAcceptClicked} label={_t("Accept")} />
  </div>);
  }
  } else { // request sent by us
  