broadcasts (#2707)

* 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>

src/stock_str.rs

@@ -311,6 +311,9 @@ pub enum StockMessage {
 
     #[strum(props(fallback = "Messages"))]
     Messages = 114,
+
+    #[strum(props(fallback = "Broadcast List"))]
+    BroadcastList = 115,
 }
 
 impl StockMessage {
@@ -985,6 +988,12 @@ pub(crate) async fn messages(context: &Context) -> String {
     translated(context, StockMessage::Messages).await
 }
 
+/// Stock string: `Broadcast List`.
+/// Used as the default name for broadcast lists; a number may be added.
+pub(crate) async fn broadcast_list(context: &Context) -> String {
+    translated(context, StockMessage::BroadcastList).await
+}
+
 impl Context {
     /// Set the stock string for the [StockMessage].
     ///