feat(GoodConf): generate TOML configuration for complex types

[mion00]

Description

• Refactor generate_toml() to recursively traverse the various input fields, generating TOML list and tables to contain nested classes and list of other elements, until a base type is found.
• Refactor initial_for_field() to invoke dict() method on BaseModel classes, or to handle nested lists
• Add tests containing nested config classes and lists

Fixes #32