removes unused object properties pointing to LoginForm etc on HomePage
adds GameBackupList widget to HomePage
uses gameDetails.isInProgress in Game constructor instead of checking for a result
adds Game.getBackupDetails for backing up and restoring games. it
returns only the data needed to restore the game and verify that
both users are talking about the same game.  draw offers and undo
requests are not preserved.
refactors history initialisation to use map() instead of forEach in Game
stores options on Game as _options; uses that reference in timingStyle set up
initialises gameBackups as empty object instead of empty array in the db in User
uses game.getBackupDetails in User._saveGameBackup instead of trying to just store the game directly
renames backups to gameBackups in Ractive template in GameBackupList
adds isInProgress to Game.getBackupDetails
renames game_restoration_ classes to game_backup and adds :id to Ractive enumerator directive
to make it go over the object
uses display:none to hide game restoration dialog so that there is always
a reference to it from _template.nodes (otherwise trying to add the
GameBackupList to it doesn't work, as the parent element doesn't
actually exist if it's in a Ractive conditional directive that isn't
satisfied)