Prevent duplicate comments on issues to be inserted

[rajbos]

We currently insert comments, even if they have already been added. This might be confusing for the user.

How can we improve this? Some idea's:

1. Delete existing comments for clarity. We can probably use different emoticons for each message, and thus remove the old comments before we inject a new one.
2. Don't add a new comment when there is already an existing one. Update the existing one?

Input welcome!