See the first github-wide commit for a user

[xavierlacot]

The project works great and allows to see the first commit for a given project.

It would be great to also find the first commit for a given user github-wide (the user "lambda" may have made his first public commit a long time ago in the repository "alpha/beta", it would be nice for him to be able to find it again). For organization usernames (ie. "premieroctet") who cannot have authored a commit, we could display the first commit ever made in a public project within the organization