Add a method to scramble the variable names in a model

[d-krupke]

The variable names can tell a lot about a model, which can be bad for models from a partner. It would be great to have a function that can just rename all variables in the protofile by some random name. Should not be too difficult.

This way, one could use these models more easily in a benchmark set for this tool without having to worry about accidentally leaking information in the variable names (imagine you have a nurse scheduling problem and the nurse's name appears in the variable name).