Easier access threads by remove public-members, show message in channel on send

This way you can join any thread by removing the join functionality, so you'll keep access on unarchive.

It would be cool if you can ask permission to join private chat's (in public channels), but there this isn't about now.

Further it would be nice if for public channels, a message overlay appears under the name-thread-bell-pin-member-more-button bar of the channel it belongs to.