axisLabels with better example

[ax3l]

Backwards compatible enhancement (before #129 can be implemented, which would break backwards compatibility).

The writing in axisLabels (and gridSpacing, etc.) should be as with the bracket indexing method that wrote the record.

E.g., a C-style E[z,y,x] with dataOrder='C' would be axisLabels="z;y;x" (PIConGPU). Warp uses C-style indexing E[x,y,z] with dataOrder='C' which would be `axisLabels="x;y;z".

A Fortran code E[x,y,z] with dataOrder='F' would write axisLabels="x;y;z".