* add Chattype::Broadcast and create_broadcast_list()
* do not disclose recipients for broadcasts
* allow sending/add-/remove-member for broadcast
* set broadcast subject same as for one-to-one chats
* broadcast-recipient-list does not include SELF
* use special icon for broadcast groups
* generate initial broadcast names
* make clippy happy
* send BCC message unencrypted to avoid unexpected disclosing; encryption is opportunistic anyway. if we have 'protected chats' at some point, we can think that over.
* reword 'To:'-group
* simplify can-send-check
* add broadcast tests
* tweak comments
* Update deltachat-ffi/deltachat.h
Co-authored-by: Hocuri <hocuri@gmx.de>
* change name of can_edit() to is_self_in_chat()
Co-authored-by: Hocuri <hocuri@gmx.de>
