send mention notifications on comment update

[nitely]

Changes:

• Create/update mention on comment update/edit if the comment's date is greater/equal than the notification's date.

The comment's date is always the same regardless of updates, so it should be ok. If the comment is older than the notification then that comment is already read, so I think there is no point in updating the notification. If the comment is way newer than the notification and there is a bunch of unread comments in the middle that should not matter. It's how mentions have always worked.

Needs tests before merging this thing

[coveralls]

Coverage increased (+0.0003%) to 97.374% when pulling 645f05c on feature/mention_notification_on_comment_edition into 9ae914c on master.

[coveralls]

Coverage increased (+0.0003%) to 97.374% when pulling 645f05c on feature/mention_notification_on_comment_edition into 9ae914c on master.