Suggestion: Add option that disables peacefulness for Capital towns

[VRILGQD]

Feature Request
Add an option in the Towny config that disables /t toggle peaceful for capitals of a nation.

Why I am Requesting This
Many people on my server have massive nations that try and exploit peaceful mode to avoid sieges. I think if an option that prevents capitals of a nation from going peaceful existed, these problems would start to go away, since nations would have to be more geopolitically active.