* Use Regex#match?

* Replace =~ too

* Avoid to call match? from Nil

* Keep value of Regexp.last_match

* Fix HTML validation

* Report first HTML error instead on validation error

* Add validations to admin settings

- Validate correct HTML markup
- Validate presence of contact username & e-mail
- Validate that all usernames are valid
- Validate that enums have expected values

* Fix code style issue

* Fix tests