Use dbuild 0.7.0. Read versions.properties.

Uses the new 'assemble' build system.

Tested by: https://scala-webapps.epfl.ch/jenkins/job/pr-scala-integrate-ide/3922/consoleText

As witnessed by:
```
From git://github.com/adriaanm/sbt-builds-for-ide
 + 66710ff...35afb80 master     -> remote03/master  (forced update)
```

review by @jsuereth, /cc @cunei, @skyluc