Merge develop to master

This MR includes changes for multiplexing modes: The goal with these changes is to introduce a method of calculating the number of multiplexing modes. This is done by adding two new parameters and a method in the SPDC class. Furthermore, I have added separate parameters for the number of multiplexing modes for the source and the memory, and a method of finding the number of multiplexing modes for the whole system. Finally I have changed tests to fit this parameter and added a new to to check the calculations.

Some additional changes to the dependencies have been made:

• Remove pickle5 dependency
• Replace pickle5 usages with pickle
• Restrict pandas to be <1.5.0