Backup improvements & example

XXMessengerClient library

• Fix race condition issues when starting the backup and setting initial parameters.
• Add BackupStorage utility that can store the backup.
• Store BackupStorage.Backup on disk.

xx-messenger example

• Start backup
• Resume backup
• Stop backup
• Store backups in storage
• Observe backup storage
• Export backup from storage
• Resume backup on launch

.gitlab-ci.yml

@@ -13,10 +13,26 @@ before_script:
 stages:
   - test
 
+test-package-macos:
+  stage: test
+  tags: 
+    - ios
+  script:
+    - ./run-tests.sh macos
+  retry: 1
+
 test-package-ios:
   stage: test
   tags: 
     - ios
   script:
-    - ./xcode-remove-caches.sh
     - ./run-tests.sh ios
+  retry: 1
+
+test-examples-ios:
+  stage: test
+  tags: 
+    - ios
+  script:
+    - ./run-tests.sh examples-ios
+  retry: 1