Random scenario selection options

Add two options in the World Defaults menu to enable random scenario selection for random characters.

Options:
- Random character and scenario  
- No challenges

This PR is a follow up to https://github.com/CleverRaven/Cataclysm-DDA/pull/9696.
I'd default this to True, as we don't expect Challenges to lead into typical gameplay.  (For example, we make no particular effort to make the Locked Lab escapable--in fact, we removed teleport labs from ground floors to prevent people from instantly escaping.)

Basically, folks should opt into a Challenge, either by manually picking it or via removing the safety lock here.