Materialize the number of finished builds

The NrBuilds table tracks the value of ‘select count(*) from Builds
where finished = 0’, keeping it up to date via a trigger.  This is
necessary to make the /all page fast, since otherwise it needs to do a
sequential scan on the Builds table.

src/lib/Hydra/Controller/Root.pm

@@ -155,6 +155,7 @@ sub get_builds : Chained('/') PathPart('') CaptureArgs(0) {
     $c->stash->{allJobs} = $c->model('DB::Jobs');
     $c->stash->{latestSucceeded} = $c->model('DB')->resultset('LatestSucceeded');
     $c->stash->{channelBaseName} = "everything";
+    $c->stash->{total} = $c->model('DB::NrBuilds')->find('finished')->count;
 }