WorkflowKernel - createVersion - new date field

[rsoika]

If the WorkflowKernel method createVersion() creates a new Version a new Date item should be created indicating the point of time. This is needed because the $version item is overtaken as it is (which is also important for the revision process)

$created.version

This can be helpful for applications to show the date in a chronical view like in Imixs-Office-Workflow

Note:
This change has no effect on older workitem instances and does not need any migration strategy!