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 tested it in a 80x25 terminal and it fits on the screen. I didn't notice before, but what the key does is already being explained under the help on the description page when pressing '?'.