This commit adds the ability to onebox private GitHub
commits, pull requests, issues, blobs, and actions using
a new `github_onebox_access_token` site setting. The token
must be set up in correctly to have access to the repos needed.
To do this successfully with the Oneboxer, we need to skip
redirects on the github.com host, otherwise we get a 404
on the URL before it is translated into a GitHub API URL
and has the appropriate headers added.
Linking a commit from a GitHub pull request included the complete commit
message, instead of just the first line. The rest of the commit message
will be added to the body of the Onebox.
Loïc Guitaut
Martin Brennan
Jarek Radosz
David Taylor
Bianca Nenciu