Mention users

[driesvints]

People should be able to mention users in replies and threads with an @ tag. Upon thread or reply creation, these tags are detected and the user mentioned gets an email notification. This should only happen for thread or reply creation and not with updating them. User mentions in threads and replies should be indicated with a link to their profile and be styled as bold.

It's also important that we provide a way for users to unsubscribe from notifications on a thread. Atm a reply to a thread they're subscribed to already sends a notification.

So basically if a user is mentioned in a thread:

1. and they aren't subscribed yet to the thread, they're being subscribed
2. they receive a specific notification/email for the mention: "X has mentioned you in a thread"
3. they can unsubscribe again from the email in the same way the current reply-notification offers

We should probably also think of a way to prevent abuse. GitHub implements this as an opportunity to block a user. But that's for a different solution.

[wilburpowery]

Anyone working on this? @driesvints, I can give it a shot.

[driesvints]

@wilburpowery I'm currently working on implementing subscriptions. I guess when that's done this can be picked up.

[driesvints]

Sent in a tiny part of this in here: #643