Extend user data with email

[kulasekp]

The email should be:

• required when new user is added or existing one is edited
• should be included in CurrentUser
• unique and not null - it should be implemented on UserManager level (see validate).

Additionally:

• we should avoid static usages of SecurityContextHolder.getContext().getAuthentication(). Instead please define AuthenticationService with CurrentUser getAuthenticatedUser() method. Should be registered as Spring bean in WebSecurityConfig