FIFO ordering of input events (#1386)

* Initial FIFOing of roomserver inputs

* Remove EventID response from api.InputRoomEventsResponse

* Don't send back event ID unnecessarily

* Fix ordering hopefully

* Reduce copies, use buffered task channel to reduce contention on other rooms

* Fix error handling

roomserver/api/input.go

@@ -83,5 +83,4 @@ type InputRoomEventsRequest struct {
 
 // InputRoomEventsResponse is a response to InputRoomEvents
 type InputRoomEventsResponse struct {
-	EventID string `json:"event_id"`
 }