Move "/tensorflow_graphics/projects" to "/projects"

[taiya]

Currently "projects" are stored under the TFG namespace. On the other hand "submodules" are not, creating an inconsistency.

This has two main effects:

1. long python import statement import tensorflow_graphics.projects.project.foo.bar
2. the pip dependencies of projects need to become tensorflow_graphics dependencies (overkill?)

Recommended actions:

1. We should move the projects subfolder to the root
2. We need to make sure subprojects are properly tested (1x github action/project?)