[maven-release-plugin] prepare for next development iteration
Merge branch 'release/0.3.1' into develop

* release/0.3.1:
  [maven-release-plugin] prepare for next development iteration
  [maven-release-plugin] prepare release v0.3.1
revert to Java 1.6
[maven-release-plugin] prepare release v0.4.0
Merge branch 'release/0.4.0'

* release/0.4.0:
  [maven-release-plugin] prepare release v0.4.0
  revert to Java 1.6
  [maven-release-plugin] prepare for next development iteration