Parameters (not for refinement) given to the Control Object aren't passed to the Minimizer.

The control object takes a set of parameters and passes the ones relevant for refining to the minimizer. The condition for whether ithe parameter is 'relevant' is linked [here](https://github.com/MDMCproject/MDMCv0.2_pilot/blob/64ddf6e8b11bf82da02469e909d19320d66f05e9/MDMC/control/control.py#L204-L205).
The only documentation for this is the code comment above it and a brief explanation in the doc string of the control object. It would be best to better document this process. MDMC disregarding any parameters that are set to 0 needs to be a better documented 'feature'.

In the Argon script (and possibly others) 'charge' is stored with the fit_parameters variable and passed to the control object this way. Argon is neutral and so this charge value is correctly set to 0, and therefore not passed to the minimizers for refining. Whilst the control object correctly can differentiate between a parameter than needs refining and otherwise, it is still 'odd' for it to be stored in fit_parameters in the first place, when its known that no fitting is required.