extract user urls from profile description text in all silos

[snarfed]

we currently only do this for twitter, but we should do it for the rest too...maybe?

the concrete use case here is FB pages. for FB users, the profile web site field is a textarea that lets you enter multiple URLs separated by spaces or newlines. for FB pages, you can only enter a single URL. specifically, for http://facebook.com/indiewebcamp that's obviously http://indiewebcamp.com/, but we also want to include https://kylewm.com/ since indie events are posted there.

current status of each silo, checked if we think we're doing enough:

• twitter: profile website field (single) and text description (twitter: extract actor URLs from profile description #322)
• facebook users: profile website field (multiple), about, description
• facebook pages (support facebook pages as accounts #41): profile website field (single), about, description
• google+ users: profile link fields (multiple)
• instagram: profile website field (single), bio
• flickr: ? (ask @kylewm?)

cc @tantek @kevinmarks @kylewm who know more about silo patterns and expected behavior than me, especially whether this would be appropriate.

[snarfed]

screenshot of G+'s Contributor to section, which i think we don't currently pull from but should:

[snarfed]

scratch that, we actually are pulling from the G+ contributor section. the api unifies them all in the urls field.