adds date to game backup title
adds margin between game backups in GameBackupList
adds padding to history and border to controls in game backups
refactors dialog showing/hiding on HomePage to use a property with the dialog name or null
adds boards to game backups in GameBackupList
adds formatDate function to Ractive on GameBackupList for formatting the game start date
adds handler for select_move in GameBackupList to click through the history
stretches modal dialog overlay to fill whole screen on HomePage - otherwise
scrolling brings different parts of the page underneath into the gap at the
top
adds explicit height, overflow-y: scroll and position: relative to game backup list container.
this approach works (position: relative is needed so that the boards position relative to
the container and follow it as it scrolls, instead of to the modal overlay (which is its
next positioned ancestor and makes it stay still relative to the viewport)).  a better way
might be to use flex and flex-grow to give it variable height.
removes title and explanation paragraph from restore games dialog on HomePage
removes extra newline from home_page.css
adds logic for not hiding the dialog if it was the last thing to be clicked in HomePage