Integrate gsplat into meshroom

[Alxiice]

• Add a folder alicevision with all files required to use the tool in meshroom
  • Some of the code come from the example folder (files simple_trainer and simple_viewer
  • Replace the dataset part with a SFM loader
  • Add a initializeSplats method to initialize correctly splats from the meshing node
• Add a folder scripts with the 3 scripts that are used by mrGSplat