added link to jinja
Fixed bug where one screenshot would be incorrect

Four words: more python less javascript
load pages list in json
make preview.py use pages.json
Added comparisons for centered interface

Very hacky - when looping over interfaces, postmodern is not included.
Instead, we render a copy of it alongside each of the other interfaces,
hard-coded, with a possibly different stylesheet each time (set in
sheets.json).

This is to allow the possibility that users of one stylesheet might be
migrated to one of several descendant sheets depending on their
interface of choice.