Tidy up the SBT project definition a little.

I was rereading it so I cleaned it up some.
Stage has changed on build agents
Stage has changed on build agents
Merge pull request #1027 from guardian/project-definition-tidy

Tidy up the SBT project definition a little.
Fix the packaged jar name. Thank you SBT for that.
Merge branch 'master' into comment-counts