[Extractor] Provide an escape hatch in case of extraction failure

[maxpatiiuk]

While Readability.js generally does very good job, sometimes it fails.

Google's DOM Extractor is generally worse, but in some cases when Readability.js fails, it is a useful fallback.

Options:

• Add DOM Extractor to text-hoarder as a fallback mechanism when Readability.js didn't extract content?
• Keep reporting bugs to Readability.js for when they fail to extract a particular website?
• If text extraction fails, but alternative browser extension works well, make it easier to extract content from the alternative extension?
  • Some readable extensions spawn an iframe - any way to get inside of that?