Allow users to subscribe to 'notes' without having to comment on them

[rickmastfan67]

With the new changeset feature where you can leave comments (#772), or subscribe to one to see if somebody else leaves a comment, I would love to see the 'subscribe/unsubscribe' feature brought over to the Notes as well.

This would be very helpful if, say, a bridge had to have an emergency closure because a pier settled and somebody else created a note about it before you did. As of right now, you would then be FORCED to comment on said note just to be subscribed to e-mail notifications. It would be a lot easier if there was just a button to subscribe to it like changesets have now so you weren't forced to make a comment if you didn't want/need to.

[donaldrnoble]

I agree this would be a nice feature, but it is relatively easy to make a short moment if you are interested, so not a massive issue

[gravitystorm]

Implemented in #5284, #5304, #5310, #5314, #5346.