Build with Tycho 0.23.1

Tycho 0.23 is released [1].

[1] http://wiki.eclipse.org/Tycho/Release_Notes/0.23

We should move parent pom, target platform builds, and other places where tychoVersion or tycho-version is set) to use the latest version.

This would also include releasing a new version of repo-utils and everything else in jbosstools-maven-plugins [2].

[2] https://github.com/jbosstools/jbosstools-maven-plugins/tree/master/tycho-plugins