#412 Pool0DExpChannel has some unused attributes/methods (with bugs)

[marc]

Pool0DExpChannel has some unused attributes/methods (with bugs).

Method append_value(...) from Pool0DExpChannel is never called. Inside this method, the attribute self.cumulation is used, but this attribute is never initialized (this is a possible bug if this method 'append_value' was used).

In this class the property 'accumulation' is defined. Figure out if it exist a mix between 'cumulation' and 'accumulation' names. Reimplement code with a single naming if this is the case.