Bugfix: Dividing complex Spectrums did not work
Improvements to the averaging algorithms
 - Restructure the averaging classes' code
 - Add the simple SumDirectly algorithm
 - Do unit tests with complex values (and fix bugs that have not been discovered with floats)
 - Remove the factory
 - Rename the algorithms

API-Changes:
 - The algorithms have been renamed
    - AverageList is now SumList
    - SumAndDivide is now SortedSum
 - the sumpf.helper.average.factory() function has been removed

Note:
The SumDirectly algorithm seems to perform better than the more sophisticated
SortedSum algorithm, which was not expected. This renders the SortedSum
algorithm pretty much useless. It was nevertheless left in the sources for
further tests and future improvements.