GUI for forked data

[gmaclennan]

I have been thinking about the best way to present the concept of forked data to the user, in a way that is easy to implement without a major re-write of iD codebase.

I think one way that might work would be to still only present the most recent fork to iD via the API, but add an attribute forked=true. We could modify the iD render code to add a highlight around features with this attribute, and add a filter to only see these features. In the info pane for these forked features (the info pane is the pane on the left which displays the tags and icon) we could present a list of forks, and then use the existing iD editor conflict resolution UI to review those forks and choose to merge.

We would also have to deal with the case of forked features where one of the forks is deleted: i.e. one user has edited a feature when another has deleted it. I think we should preset the most recent change, but if the most recent change is the delete, then we should show the feature greyed-out with the same highlight as any other forked feature.