Changes

Invitation improvements

1) ClazzInviteViaContactScreen on web: fix handling of backspace. Remove redundant extra state variable. Add key on react component.
2) ClazzInviteViaContactScreen on Jetpack compose: minor documentation improvements and handle chip removal using list (just in case multiple chips are removed, avoid multiple state updates from one event)
3) SendInviteUseCase is an interface with an implementation for the client (which sends the request to the server) and a server implementation which actually stores the invitations in the database and sends emails etc.
4) Remove CheckContactTypeUseCase - this was really duplicating the logic already contained in ParseInviteUseCase. Parse invite use case was using a string and splitting, CheckContactTypeUseCase was using a list of strings. No need to have two with essentially identical logic.
5) Parse invite use case now accepts commas and semicolons as separators
 (commit: c34db32)