NLeSC/Xenon: Xenon 1.2.1

Xenon 1.2.1 This is release 1.2.1 of Xenon. Bugfixes: fixed nasty inconsistency in adaptor implementations of waiting for jobs to start or finish. What's missing: The GridFTP adaptor is not considered stable yet. It is not part of this release. There is no adaptor writing documentation at the moment, nor is the Javadoc complete for the internals methods of the adaptor implementations. It should be made easier to inspect at runtime which adaptors are available and what properties they support. We can always use more adaptors, e.g, for S3, SWIFT, HDFS, YARN, Azure-Batch, Amazon-Batch etc. These are planned for 1.3 or later. We can always use more interfaces, e.g. for clouds. This is planned for 2.0