Support version history access via the handle node

When a preview variant is created (which is versionable), add to the hippo:handle a String property that has the UUID (or path if needed) of the jcr:version history root node of the preview variant : This way, we can access version history of a document without requiring to go through the preview variant. If possible we should try to make this a single transaction although I am not sure whether the version history node already exists before the preview is persisted. If not, I am not sure what the getIdentifier of a newly created preview node which is not yet persisted returns. The identifier in turn specifies the jcr path in version history where the node can be found (and thus we could store the path of the jcr version). To be tested.
The above should be integrated into the community workflow

Idea to add a new mixin:

hippo:versionInfo

This mixin contains two properties (afaics for now)

# uuid (or path?) of the version history node
 - hippo:versionHistory (String)
# contains the labels that have been used in the past for revisions. Some labels might