Updated our build to use Zinc artifacts

Updated our build to use the Zinc artifacts built and published by dbuild.  The
main advantage is that we no longer need to build and publish the Sbt artifacts
(which are exactly the same used by Zinc) that are used in the Scala IDE for
incremental compilation.

/cc @jsuereth

Before merging this, I'll have to 

* update the uber-build script.
* update the developer documentation.

Also, I'd like to backport this change to release/3.0.x right away