[ansel] Ansel::listGalleries()

[Ben Chavet]

> As Heath suggested, hashing is a good idea. I'd do it on the first
> character of
> the  datatree_id that the image gets, which will be a hex value (a to f).
> That's 16 buckets; if necessary we could then hash those buckets on the 2nd
> character of the name, which would be 256, which is probably enough. :)

Hashing is good, now for the details :)

do we want:
   ansel/hash/image_full
   ansel/hash/image_screen
   ansel/hash/image_thumb

or:
   ansel/full/hash/image
   ansel/screen/hash/image
   ansel/thumb/hash/image

I personally like the 2nd option because it just feels cleaner.

--Ben