message: Add tooltip to collapsed sublists
diff: @@ -561,6 +561,11 @@ export default class RoomSublist2 extends React.Component<IProps, IState> {
  </div>
  );
  + let Button = AccessibleButton;
  + if (this.props.isMinimized) {
  + Button = AccessibleTooltipButton;
  + }
  +
  // Note: the addRoomButton conditionally gets moved around
  // the DOM depending on whether or not the list is minimized.
  // If we're minimized, we want it below the header so it
  @@ -569,7 +574,7 @@ export default class RoomSublist2 extends React.Component<IProps, IState> {
  return (
  <div className={classes} onKeyDown={this.onHeaderKeyDown} onFocus={onFocus} aria-label={this.props.label}>
  <div className="mx_RoomSublist2_stickable">
  - <AccessibleButton
  + <Button
  onFocus={onFocus}
  inputRef={ref}
  tabIndex={tabIndex}
  @@ -579,10 +584,11 @@ export default class RoomSublist2 extends React.Component<IProps, IState> {
  aria-level={1}
  onClick={this.onHeaderClick}
  onContextMenu={this.onContextMenu}
  + title={this.props.isMinimized ? this.props.label : undefined}
  >
  <span className={collapseClasses} />
  <span>{this.props.label}</span>
  - </AccessibleButton>
  + </Button>
  {this.renderMenu()}
  {this.props.isMinimized ? null : badgeContainer}
  {this.props.isMinimized ? null : addRoomButton}
  