gemini3d/mat_gemini: better plotting, auto-download equilibrium, less resource usage

make 3D plotting more functionalized and use R2020a save figure enhancements when available plotall: option to specify number of parallel workers writedata: less required inputs download equilibrium data if eq_zip and eq_url are specified Efield: loosen input requirements run: shutdown parallel pool before Gemini to save a lot of RAM setup_functions nml variable allows character array of function names to be used loadframe: tolerate partial variable set writegrid: auto file_forma