Display a "welcome" message when a user hasn't submitted a patch or commented before

[johnbillion]

We have a really useful feature on our Trac which shows a message at the bottom of a ticket when the ticket is created by a user who is new, IIRC if it's only the user's first, second, or third ticket. The message reminds the reader to be welcoming to the new user.

It would be great to have this same functionality for comments and patches, too. If a new user creates their first patch and submits it to a ticket (which wasn't opened by them), I'd love to know about it so I can help guide that user. Same for comments, in case the user is doing some testing, etc.