Switch to dbuild for Sbt artifacts.

* Once this is merged, we can remove the *sbt-legacy* profile in scala-ide

This PR depends on typesafehub/sbt-builds-for-ide#4, please don't merge before.

I tested it using [pr-scala-integrate-ide-staging](https://scala-webapps.epfl.ch/jenkins/view/pr-validators/job/pr-scala-integrate-ide-staging/), and my forks for *jenkins-scripts* and *sbt-builds-for-ide*. I updated URLs for this PR, so you won't be able to reproduce those builds in the staging job until typesafehub/sbt-builds-for-ide#4 is merged.