[CIG-LONG] Visualisation of materials

[Matthieu_Quinquis]

Hi all,

I would like to visualise the materials defined on a particle, not only
it's density and viscosity. This option doesn't seem to be implemented
for the moment in GALE. 

I've tried to add this to the VTKOutput plugin, but I'm having some
difficulties. I'm not able to find the "Material flag" attached to the
particle and where it is defined in the code. 

Cheers

Matthieu