Allow users to create their own rules

[mark-wiemer]

Is your feature request related to a problem? Please describe.
As a user,
I want to be able to create my own rules.
That would be really fun for me.

Describe the solution you'd like
Let me input a rule somehow to the program and then create levels using that rule. Ideally, the rule is persistent across runs.

Describe alternatives you've considered
Right now, as a user, I can't create my own rules at all.

Additional context
N/A

Acceptance criteria

• I can create my own rules within the Solver control flow (currently main.Main)
• Bonus: The rules stay persistent across runs