Updated script for 4.0.0-b03 release

* Added new SBT_IDE_VERSION variable to be able to inject
  the version of the Zinc artifacts needed to build the IDE.

* Both SBT_VERSION and SBT_IDE_VERSION should be non
  empty when building a release. This is done to avoid we
  inadvertently use the default value defined in the POMs
  (which are good for nightlies, but not for releases).
removed useless release_indigo.sh.sample