Add a lobby tooltip to topbar on mobile

app/src/components/Controls/TopBar.js

@@ -480,6 +480,34 @@ const TopBar = (props) =>
 							<MoreIcon />
 						</IconButton>
 					</div>
+					{ lobbyPeers.length > 0 &&
+					<Tooltip 
+						title={intl.formatMessage({
+							id             : 'tooltip.lobby',
+							defaultMessage : 'Show lobby'
+						})}
+					>
+						<span className={classes.disabledButton}>
+							<IconButton
+								aria-label={intl.formatMessage({
+									id             : 'tooltip.lobby',
+									defaultMessage : 'Show lobby'
+								})}
+								className={classes.actionButton}
+								color='inherit'
+								disabled={!canPromote}
+								onClick={() => setLockDialogOpen(!room.lockDialogOpen)}
+							>
+								<PulsingBadge
+									color='secondary'
+									badgeContent={lobbyPeers.length}
+								>
+									<SecurityIcon />
+								</PulsingBadge>
+							</IconButton>
+						</span>
+					</Tooltip>
+					}					
 					<div className={classes.divider} />
 					<Button
 						aria-label={intl.formatMessage({