Generalize code to not be so opinionated

[Correct-Syntax]

Right now, the nodegraph is very opinionated for Gimel Studio's purpose. We should move the non-general code to Gimel Studio itself and change the api to allow gsnodegraph to be used for other projects.

A few rough ideas:

• Make "hooks" to allow custom stuff to be drawn on nodes, etc
• Make the widget to not be so opinionated in how it reads properties, how the registry is setup, etc