Config: default & serialization

[bitsandfoxes]

Two main goals:

1. Set default values at the appropriate time
2. Set up a user-facing options object to deal with overrides and other limitations (i.e. serialization)

I created a new class for the user-facing options object and decided to go with unity's scriptable object. That way we completely avoid any serialization/deserialization on our part + it's editable in the inspector (if we choose to support that).

[bruno-garcia]

first pass