Add material visualization for TileCal

This MR adds the materials used for Tile in rel.22 to gmexMatVisAttributes.json. With these additions, Tile geometry is visualized as in VP1¹.

Before the extra definitions:

After the extra definitions introduced with this MR, where 7 materials have been declared:

The newly defined materials are:

• std::Air
• std::Iron
• std::Aluminium
• tile::SiO2CondEpox
• tile::Glue
• tile::Scintillator
• LArServices

I left out the definition of LArIronBox because I didn't want to make it look like std::Iron. We can choose a color for it later.

---

Note:

At a later stage, we need to decouple the experiment-specific material names/definitions to additional files, which the user can specify when launching gmex.

[Probably, the files containing the ATLAS materials could be stored in the GeoModelATLAS or GeoModelDATA repositories. To be discussed]

---

Footnotes:

1. (Almost identical to VP1: I found, in fact, that in VP1 the scintillator is colored as greenish, while for the moment I only found a definition for a blueish "Scintillator" color; but, nevertheless, the material is visualized differently than the surrounding volumes, which is the important thing so far) ↩