Automatically search instead of prompting the user

[SidneyNemzer]

Background: When GIT REVEAL finds a site with a server: github.com header and a custom domain (not *.github.io), we know it is a GitHub pages site. Currently GIT REVEAL gives the user a link to search Github for the domain. Since Github requires a CNAME file with the domain in it, there's a pretty good chance we will find it with a search.

New Feature: Instead of giving the user a link, GIT REVEAL should use the Github API to perform the search. The GitHub search API has pretty strict rate limiting, so there will need to be logic to fall back to showing the search URL if we have hit the limit.

Implementation notes:

• It is possible multiple repositories have a CNAME with the domain. We should sort by "least recently indexed" because that should give us the oldest file, which is likely the repository that the site points to. (The search URL we give the user should do this too, if possible).
• CNAME files might have multiple domains (example)
• If the search returns no results, we can be confident that the repository is private
• We cannot tell if the repo is private but there are other results. This is probably rare though.
• Maybe this search should be delayed until the user clicks on the extension. We can set the icon to active when the header is detected. The outcome might not turn up a result, so maybe the icon should change to orange in that case.