Validate username/realname entries in frontend

[mattwebbio]

The usernameRegex and realNameRegex tests (performed on add and edit of user) in the user-service should be duplicated and errors should be displayed inline, blocking API call until validated.

Tests located here: https://github.com/plantlogic/user-service/blob/master/src/main/java/edu/csumb/spring19/capstone/services/UserService.java

Should be implemented here:
https://github.com/plantlogic/frontend/tree/master/src/app/user/management/add-user
https://github.com/plantlogic/frontend/tree/master/src/app/user/management/edit-user