Generalization of dimensions names on nexus and npz loading function.

[tuliohlgc]

The program, so far, calls the dimensions of npz and nxs files by name instead of index in some parts of the code i.g Gui_3d.
We want to generalize so the loader receives files with any dimension names.

[AmineWahada]

This is only the case in Main.py. The 4d panel doesn't treat it by name although I named the different variables energy,kx,ky and so on. Will change also the variables later to general form. In the the 3d panel, any dimensions of the input data will show up