Adding Gaussian Splatting + removed Inria code + authlib replaces Google Sign-In

[JeS24]

See the commit messages for all the changes. Some are listed below:

• Added Gaussian Splatting pipeline (nerfstudio-based - splatfacto) + web viewer.
  • With regularization, density filtering, floater removal, etc.
  • ~Uses Splatfacto-Wild (unconstrained scenes)~ (Removed due to bugs, will wait for splatfacto to add stable support)
• Added support for Authlib to get rid of Google Sign-In's cookie and tracking problem. (WoC 2024)
• Major & minor updates to most of backend code.
• Minor fixes & updates to frontend.