Notify citizens on argument up/downvoting

[gvilarino]

Whenever citizens' arguments are upvoted or downvoted, they should be notified

[mopkobot]

What kind on notification do you wanna use? Email, UI?

[gvilarino]

Both, actually, and expandable to stuff like push notifications, sms, whatsapp or whichever transport available in the future.

The effort's being done in this other repo and I'll be hooking it with this component.

[jfresco]

See #1126. Should we add an e-mail notification?