Enhancements for MultiInputs:
 - a replace method can be specified
 - a data container for simplifying the use of MultiInputs
 - tidied up update method in the MultiInputConnector class
The MergeSignals and MergeSpectrums modules now use the new "replace method" functionality from the MultiInput
A rewrite of the FilterGenerator class.

API-Change: This commit changes the behaviour of the FilterGenerator class
Add a module that calculates an energy decay curve from a given impulse response