Decouple JobHelper as a standalone project

[Andrey9kin]

Idea is to decouple JobHelper to a separate project so it could be reused by more instances of Jenkins without inheriting JenkinsAsCodeReference

In this way JobHelper will be built as an artifact, deployed to maven central and could be picked as a binary dependency using grab

[Andrey9kin]

Already move to the https://github.com/Praqma/jobdsl-helpers
What is left is to setup deployments to the maven central