Add StaticModel role, and add it to Commit model

Instead of doing this:

    link_to(commit.id, project_commit_path(project, id: commit.id))
    Note.create(noteable_id: commit.id, noteable_type: "Commit", ...)

It lets us do this:

    link_to(commit.id, project_commit_path(project, commit))
    Note.create(noteable: commit, ...)