Poll model - page /relations results (#3073)
* first cut poll model
* process incoming poll relations
* allow alt event types in relations model
* allow alt event types in relations model
* remove unneccesary checks on remove relation
* comment
* Revert "allow alt event types in relations model"
This reverts commit e578d84464403d4a15ee8a7cf3ac643f4fb86d69.
* Revert "Revert "allow alt event types in relations model""
This reverts commit 515db7a8bc2df5a1c619a37c86e17ccbe287ba7a.
* basic handling for new poll relations
* tests
* test room.processPollEvents
* join processBeaconEvents and poll events in client
* tidy and set 23 copyrights
* use rooms instance of matrixClient
* tidy
* more copyright
* simplify processPollEvent code
* throw when poll start event has no roomId
* updates for events-sdk move
* more type changes for events-sdk changes
* page poll relation results
* validate poll end event senders
* reformatted copyright
* undo more comment reformatting
* test paging
* use correct pollstartevent type
* emit after updating _isFetchingResponses state
* make rootEvent public readonly
* fix poll end validation logic to allow poll creator to end poll regardless of redaction
