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

Add support for sub paths and remove restriction of HTTP methods.

Fixes regression introduced by commit
7eec95ae.

This enables the manipulation of Contents before creation/update and
ContentGroups of Rooms after creation/update for API v3.

This enables the manipulation of Comments (creatorId) before creation
for API v3.

Closes !80.

This is used by RoomController to allow requests to /room/~{shortId}.

This enables the manipulation of Rooms (shortId, ownerId) before
creation/updating for API v3.

Additionally, added AnswerController for API v3.

Tom Käsler authored 7 years ago and Daniel Gerhardt committed 6 years ago

See !75.

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

A new cache 'room.id-by-shortid' has been introduced to speed up ID
lookups.

Some legacy identifiers remain very persistently.

Additionally, remove obsolete VisitedRoom repository and renamed
VisitedRoom references to RoomHistory.

Additionally, remove obsolete MotdListRepository.

Implemented migration of settings.

* 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'