Implemented function interface and refactored function based code.
removed obsolete Nullcheck.
Further refactoring utility code.
Provided documentation for extracted utilities.
Fixed documentation in utils.
Adding test cases for building multicap stations.
Merge branch 'master' into finances

Update from master with new tests to be up to date.
Fixed registering childnodes with simulator.
Refactored reporting to finanace tracker instances.
Added code and tests for payment/reward models and implementation details.
Finishing documentation.
Fixing small documentation errors. This commit closes #2.