Draft: Restore optix 5

Origin

Following #196 . Malia binaries are currently not only running on OptiX 6.5 (requires maxwell GPU or above) and the source code does not build with OptiX 5.1.1 or OptiX 6.0 due to RT Core specific code. Only the malia dedicated branch builds but is not up to date and hard to maintain.

Modifications

Cmake now detect the installed Optix version and set a compile define to use non-RT Core compliant code if necessary.

Update the doc to have download link for all versions (only windows for now, see todo).

TODO

More robust cmake to automatically use the best optix version if more than one is installed. Add more deploy CI for ubuntu. #196 may be best to adress before merging this branch.