Support for Bind mounts

Adds support for `--volume`, see [JENKINS-24683](https://issues.jenkins-ci.org/browse/JENKINS-24683). 
It does not add support for the `--volumes-from` option. I do not think this option is important and will remove the request for it from the issue for now.

During development, I found that only some of the existing help files were considered.
@vjuranek This is related to our [discussion](https://github.com/jenkinsci/docker-build-step-plugin/commit/4f4786e955daac33e49039ea4655a10a93bb0ee2), at least for the help files aspect:
If you redefine `descriptor` in the jelly file, you can keep the referenced help files next to it.