Reorganize docs and fix some small bugs

[cgokmen]

This PR:

• Moves some docs pages around
• Fixes all broken links in docs
• Replaces .html links with .md links as expected by mkdocs (the former works but mkdocs doesnt recognize them as cross links)
• Fixes config issue that makes griffe misunderstand returntypes
• Fixes typo in point goal reward potential
• Adds assertion to safeguard against uninitialized objects being saved
• Sets the default observation mode of robots to be rgb+proprio instead of the whole mess (bounding boxes are REALLY slow)
• Fixes a bug in ControllableObjectViewAPI that causes error outputs at load time