Accept Constitution before Joining a Nation

[xsttx]

Feature / Issue

When clicking on Join nation - there should be a pop up saying "Have you read and accepted the constitution? If yes, proceed and pay the miners fees on the Ethereum chain to Join the Nation" or something like that.

Acceptance criteria

When it's clear that people need to approve of the Nations constitution before joining it (because it's a mutual contract)

Additional information

Constitution is currently called "About" the Nation (see previous issue)