Increased the minimum CUDA version required

We now require CUDA 7.0, whose features help keep the code more maintainable.

Increased the minimum MSVC version required

We now require MSVC 2017, so we can rely on full C++11 support and the highest quality implementations. On this platform, we now also require CUDA 9.0.

Updated the OpenCL requirement to version 1.2

We now require at least OpenCL version 1.2 both for API and kernels. All currently targeted vendors’ libraries do support it, so this is not a restriction in any way.