Searching for Commits

Since commits don't have a simple time-ordering associated with their labeling, getting at a particular commit can be challenging. It might be nice to be able to search for commits by author, date, passing status, or commit messages. Right now you can hard code a url with a valid commit identifier, so if you do know a particular commit, you can get to it.

This would be similar to the search feature on test instances, and perhaps could be ported over to `mesa_test` as well (you could search commits from the command line).