Refactor CRUD and legacy events

See merge request !108

Replaced the following events with StateChangeEvent:
* FeatureChangeEvent
* LockFeedbackEvent
* LockQuestionEvent
* LockVoteEvent
* LockVotesEvent
* PiRoundCancelEvent
* PiRoundDelayedStartEvent
* PiRoundEndEvent
* PiRoundResetEvent
* StatusRoomEvent
* UnlockQuestionEvent
* UnlockVoteEvent

Removed the following redundant events:
* DeleteAllLectureAnswersEvent
* DeleteAllPrepareationAnswersEvent
* DeleteAllQuestionsAnswersEvent
* DeleteAllQuestionsEvent
* LockQuestionsEvent
* UnlockQuestionsEvent
* UnlockVotesEvent

To trigger events, some code was migrated to use EntityServices instead
of directly accessing Repositories.

The hook methed was never called.

The event is now published for every single patched entity.

Add modifyRetrieved hook method for DefaultEntityServiceImpl

See merge request !107

`modifyRetrieved` can be overriden to modify Entities before they are
returned by CRUD methods.

Mock the correct method.

Include ContentGroups when retrieving Contents from service

Closes #30 and #29

See merge request !106

Implements #30.
Fixes #29.

Patching of child objects is now handled.

See GH-65.

Missing dependency versions from legacy spring io platform bom are added
as properties.

Fix SpEL for score cache keys

See merge request !104

This was broken by refactoring of events.

Tom Käsler authored 6 years ago and Daniel Gerhardt committed 6 years ago

See merge request !96

State change events

See merge request !103

A new event for full updates has been added.

CRUD events

See merge request !101

The entity is now stored in a separate property.

Additionally, roomId is used instead of Room object for legacy
RoomEvents.

Refactor event handling

See merge request !100

@EventListener is used for handler methods instead of implementing
a visitor interface.

Refactor services and repositories

See merge request !99

* Prefer simple IDs over entity types for method parameters
* Avoid use of obsolete v2 classes in service and repository layers
* Optimize imports

The format for answers is now set based on the content's format.

fix comparison

See merge request !97

Fix possible null pointer dereference

See merge request !98