Up CUDA to v6

[KSepetanc]

CUDA refactored to improve startup time. Major number is upped for precaution, but the upgrade should not be breaking in any way.

[KSepetanc]

I started preparing PR for this.

CUDSS PR #144 for CUDA v6 drops CUDA.jl metapackage and only uses subpackages directly. Should we follow suit here and drop it too? Drawback I see is that extension trigger list grows to 5 packages: CUDACore + cuBLAS + cuSPARSE + cuSOLVER + CUDSS.

[frapac]

We have first to merge this PR and do a new release for CUDSS.jl: exanauts/CUDSS.jl#144

Once it is done, we can upgrade MadNLP.