add Twitter DNT sitehack

[diracdeltas]

we should consider adopting something like EFForg/privacybadger#1506 even though we already block third party cookies/referer/localstorage.

1. may prevent twitter IP address tracking and/or fingerprinting
2. useful for users who have shields down or 'allow cookies' on twitter

see https://www.eff.org/deeplinks/2017/08/privacy-badger-makes-twitter-little-less-creepy for background