message: Display RM when it = a standalone member event
  Standalone = not next to any member events in the timeline.
  fixes vector-im/riot-web#4694
diff: @@ -307,13 +307,13 @@ module.exports = React.createClass({
  for (i = 0; i < this.props.events.length; i++) {
  let mxEv = this.props.events[i];
  let eventId = mxEv.getId();
  - let readMarkerInMels = false;
  let last = (mxEv === lastShownEvent);
  const wantTile = this._shouldShowEvent(mxEv);
  // Wrap consecutive member events in a ListSummary, ignore if redacted
  if (isMembershipChange(mxEv) && wantTile) {
  + let readMarkerInMels = false;
  let ts1 = mxEv.getTs();
  // Ensure that the key of the MemberEventListSummary does not change with new
  // member events. This will prevent it from being re-created unnecessarily, and
  @@ -330,6 +330,11 @@ module.exports = React.createClass({
  ret.push(dateSeparator);
  }
  + // If RM event is the first in the MELS, append the RM after MELS
  + if (mxEv.getId() === this.props.readMarkerEventId) {
  + readMarkerInMels = true;
  + }
  +
  let summarisedEvents = [mxEv];
  for (;i + 1 < this.props.events.length; i++) {
  const collapsedMxEv = this.props.events[i + 1];
  