User collection validation
- Length of prefix
- Uniqueness of prefix
- Only alphanumeric letters
- When branded checked, then prefix not null
(from redmine: issue id 188, created on 2018-01-22tgradl, closed on 2018-02-13)
- Length of prefix
- Uniqueness of prefix
- Only alphanumeric letters
(from redmine: issue id 188, created on 2018-01-22tgradl, closed on 2018-02-13)