Better system to comment on addons

[auriamg]

Currently, there is one big textarea for admins to write comments to author into. This is not ideal, because the submitter receives the contents of the entire textbox everytime, and it may not be easy for them to tell what the email is actually about given the extra noise. We should make an improved comment system, for addons and the submitter, that works a bit like a forum - and then email notifications can be adapted to only notify people about new comments