Improve refreshing of channels / items upon launch

[cleverdevil]

When running as a PWA on iOS, after the initial launch, there isn't a way to tell the channel list to refresh, or to force Together to update the unread count for channels. It'd be great if we could detect that the PWA has been re-launched, and then immediately run a channel refresh and an update for unread counts. Alternatively, we could simply add a "refresh" button to the toolbar.