[REQUEST] add synergy set to osimx file

[cvhammond]

Is your feature request related to a problem? Please describe.
Including the synergy set used in NCP in the osimx file allows it to be parsed by synergy driven treatment optimization tools

Describe the solution you'd like
Add the as a top level .osimx element

Describe alternatives you've considered
An alternative is allowing users to transpose from one settings file to another, potentially causing issues