NSW Simulation - Finalizing changes for MT in MM code

This MR added the last step missing for MT + a few minor fixes/changes:

• All the methods involved in the MM algorithm are declared as const now (similar changes will follow with dedicated MRs for the other algorithms in the NSW Simulation), apart from the handle here... is it a problem? A feedback from experts would be very appreciated since that function is present in other algorithms as well!!
• Moved all includes to the header file for the MMLoadvariables class
• Moved the struct out of the MMLoadvariables class members and pass by reference in the code, avoiding the copy operation
• Fixed calculation for R and deltaTheta output RDO quantities

./cc @iodice @rosati @vadamico