MadAnalysis 5 - Integration of theoretical uncertainty calculation with multi-weight integration

The purpose of this project is to enable multi-weight calculations in the MadAnalysis 5 platform. The current implementation only uses the nominal weight. The secondary goal is to evaluate ideas for parallelization of compute heavy components of the project for long term contribution beyond GSoC. To preserve dependencies and avoid conflicts, I believe that a refactoring of the Weight class object is the ideal approach, functionality to combine weights shall be implemented as methods within the new Weight class, histogramming and cut-flow classes will then be modified to take advantage of the new Weight class object.