[pyramid] Fix 404 handling
Avoid seeing a traceback in the UI by catching it before it reaches pyramid and
restore usage of the '404' view.
Closes #16159863
.._TutosPhotoWebSite:Building a photo gallery with |cubicweb|========================================Desired features----------------* basically a photo gallery* photo stored on the file system and displayed dynamically through a web interface* navigation through folder (album), tags, geographical zone, people on the picture... using facets* advanced security (not everyone can see everything). More on this later...toctree:::maxdepth: 2 part01_create-cube part02_security part03_bfss part04_ui-base part05_ui-advanced