Use URLs in the sidebar

Instead of catching the click and redirecting, let the browser and
framework do the normal routing.

This eliminates complexity, although for the moment does mean we're
looping over the list instead of being able to know the offset
directly. It is still a better alternative.
Remove obsoleete bookkeeping
Fix typo
Get rid of a useless param
Don't call showGroup directly
Use groupLink() instead of by hand
Link in functions by URL
Remove unnecessary click events
More events, fewer click handlers
Merge branch 'sidebar-links'