Bug11893: Better documentation about Orion's GPU in OAR

Related to bug 11893.

• Do not put GPUs that aren't supported by Grid'5000 default environments into OAR properties.
• Print a note on Grid'5000 wiki to notify user that the related GPUs are not supported by Grid'5000 default env.
• Also, do some refactoring.

Result can be seen at : https://www.grid5000.fr/w/User:Pjacquot/test_page