Added build profile for Scala IDE for Eclipse Juno

* Updated tycho version to 0.16.0.
* New ``juno`` profile for building the plug-in for
  the Scala IDE for Eclipse Juno (default values are
  for building the nightly Scala IDE for Eclipse Indigo)
* Updated default scala.version to:
    * 2.10.2-SNAPSHOT when building against the Scala IDE 4.0.x nightly.
    * 2.10.1 when building against the Scala IDE 3.0.

Both PR validator job should finally succeed (but we can't test this until tomorrow because it looks like we have an issue with our CI server). Hopefully, it will be good on Monday.