Recaptcha: switch theme to light

dark is ugly
Redo parser

Instead of DOM -> custom and API -> custom,
it's now DOM -> API -> very-slightly-custom. The 4chan API
names and format is used, warts and all, so there's less
conversion code.

This readies the parser for extraction into a separate library.

I don't really endorse the official naming, but it's at least
documented, and better walk the cowpath than pave a new one.

Made some efficiency regressions with things like url rendering,
oh well. it'll get better soon(tm)