merge 'keywords-to-be-selected' into staging

Closes #134

See merge request arsnova/topic-cloud!58

Deleted old cleaning-function-service and implemented full comment cleaning in existing create-comment-keywords.ts

merge 'complete-implementing-profanity-filter-in-sessions' into staging

Closes #123, #122, #136, and #135

See merge request arsnova/topic-cloud!57

There are some changes in the backend
which have to be changed here to fit.

[Ticket: #142]

This commit fixes the UserRole error.
After a user enters a room,
another check is performed to ensure his role.

[Ticket: #118]

There are now many events for the room,
that can be received via websocket.