Docs: point cookie policy to Aragon Associations's privacy policy

[izqui]

AA's policy link: https://aragon.org/privacy-policy

@ganeJackS can we also update the privacy policy on the website to include *.chain.aragon.org?

Also while we are at it, please replace www.mainnet.aragon.org with mainnet.aragon.org and also add rinkeby.aragon.org, poweredby.aragon.org, convert.aragon.org, conviction.aragon.org and convert-recover.aragon.org