Post History

## Start afresh but keep history
When migrating to the Challenges category, there are several aspects of the post that could be included or discarded:

- Comments
- Edit history
- Votes

### Comments
The comments during sandbox development are not relevant to the final challenge, and would be a distraction from the conversations that happen after posting the final challenge. Leaving these old conversations displayed below the challenge might also invite further discussion of how the challenge should be designed, which is likely to be too late to change by this point.

However, it may sometimes be useful to go back and view the discussion that occurred in the Sandbox. This could be out of interest, for people interested in the history of the particular challenge, or interested in learning about how challenges in general develop over time. This would also be useful if someone questions the design of a live challenge - rather than have a discussion someone can simply link to the relevant comment thread that already reached consensus with detailed reasons why.

For this reason, I would like the comments to be preserved, but to not be present on the final challenge.

### Edit history
Similarly to comments, I think that the history of the Sandbox post is not relevant to the final challenge. In many cases the challenge design may have changed drastically during development. I would like to see only changes that happened since the point that the final challenge was posted, because these are the ones that are relevant to whether a change has unfairly invalidated an existing answer.

However, I would still like the history of the Sandbox post to be preserved. Similarly to comments, it can be both interesting and practically useful to be able to refer back to how things changed.

For this reason, I would like the edit history to be preserved, but to not be present on the final challenge.

### Votes
Similarly to comments and edit history, I would like every new challenge to start with no votes (up or down), but to still have the votes preserved in the sandbox. This can be useful for anyone interested in how various challenges were initially received in the Sandbox. It is also an easy way to verify that a challenge idea was well received, and not posted as a final challenge too soon.

## Copy rather than migrate
My thoughts on comments, edit history, and votes all point towards keeping the sandbox post around as a record. I like the idea of being able to post a new challenge from a Sandbox draft at the touch of a button, but this doesn't need to destroy the Sandbox draft.

I propose that we have a method for creating a new challenge from a Sandbox post, that leaves the Sandbox post intact as a record.

The new challenge would include the following:
- Body
- Title
- Tags
- Licence

The new challenge would not include the following:
- Comments
- Edit history
- Votes

Some additional features that would be nice to have:
- Link to the new challenge automatically added to the Sandbox post (either at the top of the body or in a new comment thread with a title like "Now posted").
- Link to the Sandbox post automatically added to the new challenge (probably as a comment to avoid distracting from the body of the challenge, although possibly using some more general future feature for links to related posts).
- Archive the Sandbox post, so it is easily available to people looking for drafts of challenges that have since been posted, but does not distract people browsing the Sandbox to give feedback. This might be future work if a more general archiving feature is implemented for other communities.