Parse a "material" keyvalue in details.vbsp

[jean-knapp]

I have a suggestion for the detail props in Hammer++. Although this might be very niche, being able to set the material of the sprite sheet in the detail prop types.

Having two separate files for handling details seems cumbersome. Reading this keyvalue from the vbsp file and overwriting what is set in the Map Properties could bring us some mega detail prop packs.