Improve the .ctf/config structure

I do not like the structure of the current ctf config. It's too basic. For example the yaml_path issue is difficult to solve because challenge keys are simple key value stores. Instead of trying to shoehorn things on top of the kv, we should break it up into more complex sections.

I think if it's possible something like this would be superior:

```
[challenges]
[test/test]
location = git@git
path = challenge.yml
```

We would need:
1. A way to detect old .ctf/configs and change behvior based on that
2. Extract the parsing behavior for both type of configs into seperate functions.