Add convenience operator to verify temporal data

[p-f]

We currently have the Verify operator that restores graph consistency by removing dangling edges.
We should have an operator for temporal data that does the same thing and additionally updates the valid time of edges.
An edge should only be valid as long as both its source- and target-vertex are valid. The following conditions should be met for any edge:

• edge.validFrom >= max(source.validFrom, target.validFrom)
• edge.validTo < min(source.validTo, target.validTo)
• maybe update the transaction time if the valid time would have to be changed by the operator?