Implemented migration of settings.

Jackson cannot instantiate non-static inner classes for deserialization.

A new service, repository and entity have been introduced to handle file
attachments to other entities. Attachments store meta data about the
file. The file upload is not yet implemented. It is planned to abstract
the storage handling to allow the support for different storage
solutions (local file system, database, cloud).

Additionally moved previously missed v2 entities to the v2 package.

Introduced content groups which replace question variants and support
sorting.

It is no longer necessary since the creator property is not serialized
for the API.

* 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`

LoggedIn documents are also handled by the SessionRepository for now.

* 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

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

Daniel Gerhardt authored 9 years ago and Tom Käsler committed 9 years ago

* Fix inconsistent whitespaces
* Remove unused imports

#14886 edited the lecture/preparation view to use new sort_question-views, saveOrder is not checking whether there is already a list

#14886 edited the lecture/preparation view to use new sort_question-views, saveOrder is not checking whether there is already a list