Add debug visualizations

Note that compiling, running or testing the first time will take a few minutes. This is because OpenGL stuff is in the dependencies, and that takes a while to compile.

Subsequent runs/builds will be as fast as usual again.

The herds map might not be as useful as I thought, given the vast amount of herds. But we may add capabilities for zoom, selection and inspection later. With the epidemic running, it may also be useful as is (with colors for that instead of the herd type...).