Upgrade to latest Commons SCXML 2.0-M1 (milestone 1)

A new milestone 1 for Apache Commons SCXML 2.0 has been provided [1] which provide large improvements over the milestone 0 tag.

Furthermore, many/most of the non-compliant SCXML Document model definitions have been refactored and brought into line with the specification.
This means we can remove our non-standard usages (specifically the _eventdata and _eventdatamap variables) and provide fully spec compliant SCXML workflow documents.

In addition, the internal API for SCXML custom Actions has been change drastically as well, but in a way which from now on should be must more resilient against future changes. So its very benefitial to upgrade to this new API now, before we release.

As this incoming change is a bit late in the game before the release tag will be set, I'll also provide and attach a reverse patch to this issue which can be applied if for whatever reason this upgrade needs to be rolled back quickly.

[1] https://issues.apache.org/jira/browse/SCXML-201