Wider field for benchmark names

I hit the 30 character limit a few times already, bumping it to 100.
New admin action for Reports: recalculate

After doing a bulk upload of benchmarks, possibly not in chronological
order, the reports might show changes wrt. to the wrong previous commit.
Then, triggering this action for all reports helps.
Aggregate report per unit_title, not per unit

If we have several very different things (Buildtime vs. Runtime) with
the same unit (seconds), we want to keep them separate.
Bugfix: Changes view for old revisions

This fixes #168.
Also include values "0" in the reports

If no value is reported, then there wouldn't be a Result object, so a
value of 0 is valid.
Merge pull request #169 from nomeata/submit

My upstreamable changes so far
Closes #168
Merge remote-tracking branch 'origin/master' into ghc