v2: Add 'order' metadata to revisions as they do have a natural
    ordering.
v3: Add a couple of utility functions to Series and SeriesRevision
v4: Provide a get_absolute_url() method on Series
v5: Add a dump() method to series, handy for debugging
v6: Use 'Series without cover letter' as default series name instead
    of 'Untitled series' to clearly indicated what's hapening to the
    user (Belen Pena)
v7: Squash in the migration (Stephen Finucane)
v8: Add (untested) manual SQL migration paths (Stephen Finucane)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Acked-by: Stephen Finucane <stephen.finucane@intel.com>