non-blocking group QR joins (#2508)

* refactor: cleanup send_handshake_msg()

- rename to send_alice_handshake_msg() as used by Alice only

- remove dead code from Bob
  (Bob's code is at BobState::send_handshake_message() since some time)

- take a contact_id and not a chat_id;
  this makes things less confusing when
  info-messages are put to the final group chat

* always directly return chat-id from dc_join_securejoin()

* take care not to create a group twice

* adapt documentation

* add info-msg on group invites; add inviter directly after creation

* document existing 'joinqr' command in repl tool

* do not create empty one-to-one chats for group-joins

* refactor: cleanup fingerprint_equals_sender()

- the function takes a contact_id directly now.
  before it consumes the first contact of a one-to-one chat -
  which may be easily confused with the group-chat in creation.
  moreover, the conversion contact_id -> chat_id -> contact_id
  is unneeded overhead.

* show info-messages in destination chat for alice

* fingerprint_equals_sender() returns Err on database failure

* tweak documentation

* clarify what an 'unfinished tasks' task is.

* add regression test for create_for_contact_with_blocked()

* rename Blocked::Manually to better fitting Blocked::Yes

* tweak test_secure_join() and make sure, Alice and Bob have only on chat after a group-join

src/stock_str.rs

@@ -326,6 +326,13 @@ pub enum StockMessage {
 
     #[strum(props(fallback = "%1$s of %2$s used"))]
     PartOfTotallUsed = 116,
+
+    #[strum(props(fallback = "%1$s invited you to join this group.\n\n\
+                             Waiting for the device of %2$s to reply…"))]
+    SecureJoinStarted = 117,
+
+    #[strum(props(fallback = "%1$s replied, waiting for being added to the group…"))]
+    SecureJoinReplies = 118,
 }
 
 impl StockMessage {
@@ -591,6 +598,32 @@ pub(crate) async fn e2e_preferred(context: &Context) -> String {
     translated(context, StockMessage::E2ePreferred).await
 }
 
+/// Stock string: `%1$s invited you to join this group. Waiting for the device of %2$s to reply…`.
+pub(crate) async fn secure_join_started(context: &Context, inviter_contact_id: u32) -> String {
+    if let Ok(contact) = Contact::get_by_id(context, inviter_contact_id).await {
+        translated(context, StockMessage::SecureJoinStarted)
+            .await
+            .replace1(contact.get_name_n_addr())
+            .replace2(contact.get_display_name())
+    } else {
+        format!(
+            "secure_join_started: unknown contact {}",
+            inviter_contact_id
+        )
+    }
+}
+
+/// Stock string: `%1$s replied, waiting for being added to the group…`.
+pub(crate) async fn secure_join_replies(context: &Context, contact_id: u32) -> String {
+    if let Ok(contact) = Contact::get_by_id(context, contact_id).await {
+        translated(context, StockMessage::SecureJoinReplies)
+            .await
+            .replace1(contact.get_display_name())
+    } else {
+        format!("secure_join_replies: unknown contact {}", contact_id)
+    }
+}
+
 /// Stock string: `%1$s verified.`.
 pub(crate) async fn contact_verified(context: &Context, contact_addr: impl AsRef<str>) -> String {
     translated(context, StockMessage::ContactVerified)