Making plugin compatible for Nexus 2.5+
Update to nexus 2.6.x

Depend on nexus 2.6.0-SNAPSHOT
Depend on app-lifecicle 1.7
Switch to Java 1.7 (nexus req)
Clean pomfile from unused properties
Update pom for nexus 2.8.0-05
Update code to work with nexus 2.8
Add an "optional" parameter
Bump the version to 1.3.1-SNAPSHOT
Simplify version provider to work around a rundeck bug
Revert "Update plugin to work for nexus 2.3.0-04"

This reverts commit 1fcc76a685a72d0955895340b5da723aa36e54d5.
Merge branch 'nexus-2.8'