Change DataObjectHandleProperty to DataHandleProperty

Move the property declaration of data handles one level lower in the inheritance hierarchy, i.e. from DataObjectHandleBase to DataHandle. The only user-visible change should be the change in type of the python configurable class from DataObjectHandleBase to DataHandle. This change will allow other types of handles (e.g. in ATLAS) to profit from the python type information.

This could be disruptive in case LHCb code uses DataObjectHandleBase in Python. We should see how large the fallout is and decide what to do. cc @nnolte who introduced the Python type information in !951 (merged).

In order to support derived DataHandle properties a small change was required in genconf to detect such cases. We should review the type inspection in genconf along what is described in !951 (comment 2994384). But that's for another MR.

cc @leggett to comment if there was a particular reason to have DataObjectHandleProperty instead of DataHandleProperty when it was introduced in !95 (merged).