VGGSfM 2.0

* More powerful camera and track predictor
* Save the GPU memory usage by around 50%
* Add Poselib as an option for Fundamental Matrix Estimation
* Support COLMAP-tyle output
* Provide focal length in pixel 
* Normalize the scene after each BA
* Remove preliminary_cameras for simplicity 
* Switch to lightglue instead of gluefactory
* Upgrade pycolmap from 0.5.0 to 0.6.1



TODO:
1. Make precision consistent 
2. Provide a step-by-step instruction for using VGGSfM for 3D Gaussian
3. Support shared cameras