Remove setHolder() method from AbstractFeature

Remove: The AbstractFeature class no longer provides a setHolder() method for changing the feature holder of a feature.
Use apache commons lang 3.x

Add: Classmod is now using version 3.x of apache commons lang.
AbstractFunctionDefinition caches executors for variants

Add: The AbstractFunctionDefinition class uses internally caches "variant -> executors" mappings in order to make creating many function instances of the same definition faster.
Properties use faster accessor functions

Add: Properties use a simple dummy function instead of initializing normal functions with complete definitions in order to skip some unnecessary and costly operations.
AbstractFunction stores unmodifiable executor list

Add: In order to prevent AbstractFunction from creating unmodifiable lists on every getExecutors() call, the class now internally stores an unmodifiable list.
Minor javadoc improvements

Fix: Made some javadoc improvements.
Update changelog