Find if accepting external OpenGL context is viable

Useful topics
- [GLFW no context hints for window](http://www.glfw.org/docs/latest/window_guide.html#window_hints_ctx)
- [SDL2 context creation function](https://wiki.libsdl.org/SDL_GL_CreateContext)
- [glfw opengl context objects](http://www.glfw.org/docs/latest/context_guide.html#context_object)
- [WGL context creation process](https://www.opengl.org/wiki/Creating_an_OpenGL_Context_%28WGL%29)

Start by reviewing the linked GLFW context hints and context-object documentation, SDL2 context creation function, and WGL context creation process. Compare how external contexts are created and managed against the project's needs. Done means documenting whether accepting an external context is viable and identifying the required scope.

Written by the indexing model from the issue text.