add account combobox to join groupchat dialog when we try to join a groupchat from another chat / groupchat. Fixes #3344

when a JID is invalid in member / admin / ... list in MUC configuration, just ignore this JID and not all others. Fixes #5241

show only once unread messages at startup when we have twice the same contact in 2 accounts. Fixes #2921

don't move selection when new text arrives and selection goes until the end of conversation textview. Fixes #5223