MGC: updates to SUSY includes for 5FS and mixing matrix helper function
Implements the following two items within the MGC SUSY pre/post includes that were previously presented during the SUSY plenary:
- Changing the 5-flavor scheme to be the default setting and including b quarks in the p and j definitions when using the 5FS
- Add a convenience function that can be called from the control file to use commonly used mixing matrices (more cases can be added in the future)