Strengthen export file safety

[DmitryBespalov]

To make the exporting safer and user more aware, implement the following:

Export Data - Instructions Screen

• Replace 'owner keys' with 'private keys': "Data includes private keys, safes and address book in an encrypted format."

Export Data - Create Password Screen

• Add "password meter" progress that shows password strength
• Require at least 8 characters for the password
• Using symbols, numbers, and capital letters increases password strength for the same number of characters.

Export Data - Success Screen

• Mention that the file includes private keys: "Exported data is encrypted and includes private keys, list of safes and address book."
• Add text "Save it to Files - On My iPhone."