Method Signatures are Inconsistent for Overridden Methods

[helegraf]

Sometimes the typing of a method in a superclass (e.g. load_dependency_inputs in Plugin) allow different types for a parameter (in that case, None, List[AbstractRun]or AbstractRun for run) whereas in the subclasses a fixed type is assumed without checking (in that case, e.g. AbstractRunfor the Budget Correlation Plugin). This should be refactored to allow consistent types.