Script framework to rearrange topics and categories

I discovered in the Retort topic that @angus has a branch with UI-driven conversion, which I had completely missed.

My script dives into internals which could conceivably change someday, and once I’ve done my conversions with this script I won’t notice if those internals change. I first tried to do it “the right way” but discovered that the Reactions plugin doesn’t expose an interface that enables this. @angus takes the longer view:

@pfaffman if you make a rake task, you might want to put it in a PR that also make the changes to the interfaces so that, for example, created_by can be passed in, as well as silent, rather than using the “back door” that I did. At that point, the rake task would be there for command-line migrations, and it would simultaneously unlock @angus doing a UI-driven migration.