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

Moved PI timer logic to its own service. The implementation for room
owner changes has been removed for now.

* 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`

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.

* 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

Fixes failing start up because of no longer existent
`security.guest.lecturer.enabled` setting.

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

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