Made changes to the DPIE model and test code as well as some changes to the...

Made changes to the DPIE model and test code as well as some changes to the execution.py so the subproblem could be handled. As of now, the execution.py file still has work I need to do to ensure it can manage single densities created as a single symbolic variable versus single densities created as a single element symbolic array. Changes to the DPIE related software has been to add some tests to help with validating and debugging the results of the DPIE code.