Messenger - backup

• Add functions to Messenger:
  • registerBackupCallback
  • isBackupRunning
  • startBackup
  • resumeBackup
  • stopBackup
  • backupParams
• Update docs
• Prevent backups without params

Docs/XXMessengerClient.md

@@ -142,7 +142,7 @@ let result = try messenger.restoreBackup(
   backupPassphrase: "backup-passphrase"
 )
 
-// handle restore result
+// handle restoration result
 ```
 
 If no error was thrown during restoration, the `Messenger` is already loaded, started, connected, and logged in.
\ No newline at end of file