JENKINS-21149 Possibility to change pipeline version in later tasks or stages

This pull request would resolve https://issues.jenkins-ci.org/browse/JENKINS-21149.

It adds an extra property on the PipelineVersionContributor to enable overriding upstream version. Also stage version has been modified to correctly pick up changed PIPELINE_VERSIONS.

Requires bumping to core 1.548 which provides Action.replaceAction() method.