Monal should use XEP-0048 Bookmark Storage to join those MUCs in the users bookmarks. Also when joining a new MUC with Monal, that MUC should be added to the bookmark list.

This gives the following possibilities:

• Only join those those marked with auto join
• Use nickname from bookmark
• Use name from bookmark to display in conversations list

(e.g. clients like Gajim and Conversations uses bookmarks and honours all those settings)