Change the edit link to a unique endpoint

[scott2b]

Users have an overwhelming tendency to bookmark the edit links of their StoryMaps. There tends to be a general impression that this is the unique link to the StoryMap, which they then share with us for support purposes.

While we can generally find the StoryMap with a bit of sleuthing, and could probably build some tools to make this a bit easier, the ID in the link is not necessarily unique. A better solution would simply to make this link unique in order to match user expectations and simplify support. Most likely, this means including the user ID within the edit endpoint.

RFC: @JoeGermuska