Fix a few things with cancelling recovery reminder
* Put a cancel button on the first page of the create key backup
dialog
* Move settings logic into the room reminder: I know this is moving
logic *into* a view but RoomView is quite heavyweight as it is.
* Give the recovery reminder an explicit 'onDontAskAgainSet' rather
than onFinished which was getting called with false when the last
screen of the dialog was closed with the cancel 'x' rather than
the 'close' button.
https://github.com/vector-im/riot-web/issues/8066
