Finish incorporate zinc

Merge the zinc dbuild in the uber-build repository, and integrate the dbuild build in the uber-build.
The uber-build does the driving of the dbuild build.

This allows to generate Scala IDE releases directly from Scala binary, and to have zinc nightly testing the integration will Scala IDE.
Zinc is now always build, expect if cached previously.

Some further improvements needed:
* being able to recover the `versions.properties` file for pre-build Scala binaries.
* have zinc-dbuild generate a more unique version for `-SNAPSHOT` builds.

@jsuereth,  there are few `sbt-on-...properties` file in the zinc folder, but I'm using only `sbt-on-2.10.x.properties` and `sbt-on-2.11.x.properties`. Do we need the other ones?

This supersedes #41.