Mark notifications as read when the corresponding action is performed

[AlbertoPdRF]

Right now, almost all the the notifications are marked as read when the page they link to is visited, but it would be better to mark them as read when the corresponding action is performed (if it makes sense, as there can be cases where it's better to leave the current behavior). The only notification that currently behaves like this is the email confirmation one.

An example: the initial notification that asks the user to upload an avatar gets marked as read when the user visits /users/:userId/edit, but it would be better to mark it as read when the user actually uploads an avatar.