Suggestion: Adding a resource production modifier for nation levels

[thespookstersaw]

Please explain your feature request to the best of your abilities:

I am suggesting adding a config option for resource production modifiers town levels have, but on a nation level as well, allowing for towns to get resource production bonuses from nations, stacking on top of the town level resource production modifier.

This could allow for a server owner to configure such things as making towns benefit from joining nations or counteracting the nation tax so towns do not lose anything from joining nations while nations still benefit from towns.