Update stronghold

[Thoralf-M]

Description of change

Update stronghold to v3

How the change has been tested

Running tests and the example

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked that new and existing unit tests pass locally with my changes

[semenov-vladyslav]

storage_password_to_encryption_key thing must definitely be fixed. There's no easy way to derive strong key from weak password and virtually no salt and iteration count.

[semenov-vladyslav]

Regarding storage_password_to_encryption_key. As @Thoralf-M explained, the key derived with it is used to encrypt public data that doesn't need thorough protection (integrity guarantees provided by the inner DB would suffice). It would be good idea to get rid of this function and respective code in the future.

[semenov-vladyslav]

A few minor changes required. Type of passwords should be unified.