Feature: add private key data safely in iCloud

[TonioMacaronio]

Current behavior:
Now you can perform backup only with your pen and paper.

Expected behavior:
It should be possible to encrypt it and add in iCloud.

Suggested solution:
You should add in BackupViewController.xib some button like "Save in iCloud" and use CloudKit to perform saving backup. Also you should encrypt it before saving and add possibility to decrypt.

Acceptance Criteria:
The code is written in new branch named feature/iCloudBackup or something like that.
The code implements the targets described above
The code can be merged into the develop branch without conflicts.

Required Skill:
Participants needs to have an experience in Swift software development.