Add more configuration options and allow setting per-URL config via tags like `depth=1`

[tjhorner]

Ideally, the options provided on the add page should also be present in the extension configuration (e.g. crawl depth and extractor methods).

In the future, it would also be nice to have this be able to be set per-domain.

[pirate]

I want to accept config options via tags as well by parsing KEY=value tags, e.g. adding a tag DEPTH=1 or EXTRACT=wget,media,screenshot,favicon,singlefile or TIMEOUT=160 should work as expected.