Include graph_using.hpp to avoid error

One ctor accepted an allocator, the other didn't

Replaced VKR template parameter with Seeds for clarity

There are a few similar definitions that are defined internally in both gcc and mscvc
that we need for the graph-v2 implementation. An issue was reported that they
weren't defined when using MSVC, so I've renamed the defintions to be unique
across the compilers to always use our own.