replace all "cmin" and "cmax" with "zmin" and "zmax" respectibly

[Stockless]

To improve consistency as requested in Issue #361 , every keyword "cmin/cmax" was replaced with "zmin/zmax" , as it was described with that notation in the keywords description for the plot_image function.

[cncastillo]

You probably need to redo this, the main problem is that

plot_image(...; zmin, zmax)

but

plot_phantom_map(...; cmin, cmax).

It doesn't really matter what they are called inside the functions, just the interface.

[Stockless]

It doesn't really matter what they are called inside the functions, just the interface.

in commit fa74970 I kept the change from cmin/cmax to zmin/zmax just when the plot_phantom_map function calls the kwargs and redefines zmin/zmax

[cncastillo]

@Stockless Did you check if all the uses of plot_phantom_map use the new syntax?

[Stockless]

None of the uses of plot_phantom_map gives cmin/cmax as an argument, there won't be any issue with the new syntax. There's also no CI test error related to this change.

[cncastillo]

Ok, add this a minor change for KomaMRIPlots to register it