Implement user name format validation

[lukasaric]

In order to improve name validation, this PR adds:

• name_format custom validation
• Validation uses Unicode regex
• Integrates it where it's needed (user first & last names)

🔍 QA note:

Check all name input validations (e.g first and last name)

[kjuej]

@malizeus Some improvement suggestions:

1. Dots apostrophes and hyphens should not appear in the beginning or end of the name
2. There should not be more than 1 hyphen/apostrophe/dot in a row.