add WebSockets with STOMP on top

See merge request !112

remove unused imports

move ws handler to websocket package

add WebSocketMessage entity structure
add basic feedback logic
add tests for Feedback messages

These tests exercise the happy path. If needed, negative tests could
be added in the future.

Ektorp's default implementation expects purge_seq to be of type int.
CouchDB 2.x purge_seq is of type String.

Reverts 8ad7cd84

This fixes issue #33. However, it is still unclear why different
beans are shared between test and production code.

Both the RoomRepository as well as the CacheManager beans were
not shared between test and production classes. Hence, when we
set up some mocks (or caches), the mocked values were not
present in the production classes.

We explicitly force instance sharing by applying the Singleton pattern.

* Update MathJax URL to use version 2.7.5
* Piwik was renamed to Matomo

Add support for OpenID Connect authentication

See merge request arsnova/arsnova-backend!118

Only OIDC providers that support configuration discovery are supported.

Google OIDC

See merge request !117

Google shuts down its Google+ Sign-In.

Add API endpoint to create copies of public pool sessions

See merge request !116

Fix import format

See merge request !115

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

The field of the inner class is kept for compatibilty reasons.

Delete inactive users

See merge request !102