Experiment with supporting >1 version.

spoilers.lua now handles this fairly well, although its multiversion handling
is done manually.  main.js doesn't work well; I can't get Finch to do what I
want.
Redo routes with Crossroads.js.  Add version dropdown.

Version dropdown is semi-functional, but changing versions fails to update
side nav, and it loses collapsed state.

For Crossroads.js, I'm manually delegating to parent routes, instead of using
Finch.js's parent routes or Crossroads' greedy.
First attempt at restoring expanded state when changing versions.

Not yet as clean of a UI as it could be.
Disable expand transitions when changing versions.
Nicer version dropdown.
Fix AJAX refresh bug
Merge branch 'multiversion'