Correlate Derived Mesh with Particle Group

[ax3l]

For species-derived fields (density, charge density, etc.) we don't currently correlate the name with the particle species.

VisualPIC as post-processing tool (@AngelFP) correlates the two in its gui, so it would be great to hint this explicitly.

One way to achive this: consistent naming scheme (e.g. PIConGPU & WarpX: <species>_<filter>_<fieldName>; FBPIC: <fieldName>_<species>).

Another way: define a string attribute on the field with the species name (nice because simple and non-breaking).

One could even define this in the base standard for meshes.