Hydrate sparse jobs after/during cron

[lefnire]

Some job boards' RSS feeds contain very limited information (just a title, link, and possibly a tiny snippet) - not enough for accurate scoring / searching. Typically their links redirect to a page full of details (company, location, tags, etc). One solution here is to set some flag hydrated=false or sparse=true or something; then after cron has finished (so we don't compete with resources) take one job at a time and scrape their links using Nightmare (there's some usage examples in the adaptors).

Known sparse boards currently: ionicjobs, pythonjobs, virtualvocations (will amend as I find them)