chat: animate dock icon

Using NSCriticalRequest makes the icon bounce to catch user attention
Icon comes back to normal when the app takes the focus.

Change-Id: I1a2504407223944775e0eac40a228bc6e5e3435d
Tuleap: #202

src/AppDelegate.mm

@@ -89,6 +89,7 @@
                          NSDockTile *tile = [[NSApplication sharedApplication] dockTile];
                          NSString* label = unreadCount ? [NSString stringWithFormat:@"%d", unreadCount]: @"";
                          [tile setBadgeLabel:label];
+                         [NSApp requestUserAttention:NSCriticalRequest];
                      });
 
     QObject::connect(&Media::RecordingModel::instance(),