Parse title from opengraph data as well

[parkr]

OpenGraph is a common way of giving a summary & other metadata about a page without modifying the title, or otherwise allowing flexibility & separation between the elements the user sees when they visit the page, and what crawlers see.

We currently only parse the title tag, but it would be neat to pull out the og:title as well.

http://www.ogp.me/

[parkr]

This would likely update this function:

radar/parser.go

Line 26 in d6a4bf7

func titleForWebpage(urlString string) string {