New Navigation UI.

I'm sure there's still lots of refinement that needs to be done here, but this
seems like a good checkpoint.

Change-Id: Ida808464c0cc40c84f7f79c016d3c6a148d50a32
Merge "New Navigation UI."
sorted: better errors when a constructor fails

Change-Id: I9cfbd6742210c3e5efae6b30c7f287d739dff7d2
thumbnails: add a cache-busting URL component, support ETag

And quiet noisy logging on normal write failures.

We can now stress test the thumbnail generation by setting
CAMLI_DISABLE_THUMB_CACHE=1 which will make all the thumbnails in the
browsers be unique, and not write them to cache on the server.

Then, when we're happy with the thumbnails, we just increment the
thumbnailVersion string and that busts all the browser- and
server-side caches.

Change-Id: I3cda8e85ab8b1b0b2c9113f6dff613dfbf736028
Merge branch 'master' of https://camlistore.googlesource.com/camlistore