Consistently use singular for packages which contain mixed kinds of
classes. Moved a few classes to packages that better fit them.

Renamed UserAuthentication to ClientAuthentication and moved it to v2.
API v3 uses its own model.

* 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'

Removed X-Forwarded header handling from the application code and
documented how to setup the servlet container and reverse proxy to
handle those.

* Moved classes from `de.thm.arsnova` root package.
* New util package
* Do not start interface names with `I`. Appended `Impl` to the
  implementing class instead.
* Renamed learning progress classes to score and move them from
  `.domain` to a new `.services.score` package.
* Do not capitalize acronyms in class names:
    * CASLogoutSuccessHandler -> CasLogoutSuccessHandler
    * SocketIO* -> Socketio*
* Renamed `.socket` package to `.websocket`

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

Consistently prioritize the `api.path` setting before falling back to
`servletContext.getContextPath()`.

Exceptions are now always passed to the logger. The logger decides based
on configuration whether and how they are logged. Logging messages were
adjusted for consistency.

Additionally, remove unused loggers.

Changed `security.facebook.enabled-roles` to
`security.facebook.allowed-roles`.

* 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

The security.*.enabled properties are now loaded as booleans.

A boxed primitive is created from a String in
* RangeAspect#handlePaginationRange()
* LoginController#dialog()
just to extract the unboxed primitive value with Integer#valueOf().
This creates an Integer object. It is more efficient to use parseInt()
which creates a primitive int.

Corrected random indention in LoginController

remove spingfox for ApiIgnore direction
use swagger-maven-plugin to generate swagger.json before compiling rather than
 dynamically generate it on request

Bug was introduced in 0d050f02.

Updated copyright year and adjusted header format to be consistent over
all files and with other ARSnova projects.