feat: key-contacts

This change introduces a new type of contacts
identified by their public key fingerprint
rather than an e-mail address.

Encrypted chats now stay encrypted
and unencrypted chats stay unencrypted.
For example, 1:1 chats with key-contacts
are encrypted and 1:1 chats with address-contacts
are unencrypted.
Groups that have a group ID are encrypted
and can only contain key-contacts
while groups that don't have a group ID ("adhoc groups")
are unencrypted and can only contain address-contacts.

JSON-RPC API `reset_contact_encryption` is removed.
Python API `Contact.reset_encryption` is removed.
"Group tracking plugin" in legacy Python API was removed because it
relied on parsing email addresses from system messages with regexps.

Co-authored-by: Hocuri <hocuri@gmx.de>
Co-authored-by: iequidoo <dgreshilov@gmail.com>
Co-authored-by: B. Petersen <r10s@b44t.com>

src/log.rs

@@ -68,6 +68,16 @@ impl Context {
         let last_error = &*self.last_error.read();
         last_error.clone()
     }
+
+    pub fn set_migration_error(&self, error: &str) {
+        let mut migration_error = self.migration_error.write();
+        *migration_error = Some(error.to_string());
+    }
+
+    pub fn get_migration_error(&self) -> Option<String> {
+        let migration_error = &*self.migration_error.read();
+        migration_error.clone()
+    }
 }
 
 pub trait LogExt<T, E>