jruby-gradle-jar-plugin is walking upright

In this changeset:
+ Jar task type extended with `jruby` closure
+ Ability to add custome gem directories
+ Ability to make a JAR executable using `warbler-bootstrap`
+ Ability to make A JAR executable supplying own main class
For now using `1+` breaks my one unittest, therefore just fixed this to a specific version. Not an ideal solution and will try to solve it. However, I still feel we need to give the user control over the version as we do for jruby-complete. So there might be more work to do.