Implemented a customized WithMockUser and
WithMockUserSecurityContextFactory to mock an Authentication with User
and UserProfile.

* AuthenticationProvider-agnostic User object allows access to common
  user attributes: userId, loginId, authProvider, etc.
* Auto-create UserProfiles for external accounts
* Use userId (instead of loginId) for permission checks
* Use custom implementation for Pac4j integration
  (remove org.pac4j.spring-security-pac4j)
* Move authentication logic from controller to service layer
* Remove user room role handling
* Rename targetDomainType 'session' to 'room'

This improves/fixes compatibility with third-party OAuth APIs.

* Remove unused code
* Optimize imports (group 10+ and static imports)
* Remove redundant variable assignments
* Replace explicit type parameters with <>
* Remove redundant catch blocks
* Use varargs instead of explicit array instantiation
* Weaken visibility of methods and fields
* Simplify conditions
* Do not use StringBuilder for simple concatenations
* Fix code style
* Remove invalid Javadoc

User object will be serialized into a String using toString() but this
should not be done in a unit test.

add type of user account
adjust test for new user account type
UserServiceTest which test persistence of the maps