Unfix the Compute Capabilities across CMakeLists

[valenotary]

The nvcc compile flags for Graphitti are fixed to CC 3.5 - which are specifically for Kepler-generation cards (around 6 years old). To enable future work in implementing newer software features and hardware capabilities, we should remove this specific flag and opt to make it flexible for newer cards (such as the Volta card on the otachi server).

This may have the drawback in having to add define macros for compiling specific sections of code, depending on whether or not the device supports a certain feature, to maintain full backwards compatibility with AT LEAST CC 3.5.

[stiber]

We should also make sure to update documentation describing how to build Graphitti, plus add a wiki page that summarizes the differences among the arch levels and specifically calls out the conditional sections of code and what the specific differences are there — ideally with some performance notes (after all, conditional compilation adds to the code's structural complexity and overall "cruft"; we should not do that if it doesn't produce a benefit).

[stiber]

Partially superseded by #902

[stardriftfx]

update documentation describing how to build Graphitti

Note: This was completed through docs quickstart.md.