Refactor map generation to enable ModInterop-based generation initiated by other mods

[corkr900]

• Refactored the generation process previously managed by button handlers in Oui code into a self-contained Builder class
• Updated Oui code to use the new Builder class
• Added ModInterop class to let other mods build a RandoSettings object without needing reflection or an assembly reference
• Added ModInterop class to let other mods initiate map generation without needing reflection or an assembly reference

These updates will be used by Head 2 Head to support randomizer races without relying on reflection