Don't sign the artifacts per default

Instead, use the release-sign-artifacts profile to sign.
Updated Tycho versions to something more recent, see also:
http://wiki.eclipse.org/Tycho_Release_Notes/0.12
Revert "Add the Scala version number to the artifact id."

This reverts commit 07b00e413d185c53332118711ff12be75f4df994.

Conflicts:
	org.scala-refactoring.library/pom.xml
decreasing Tycho to 0.12