Topic all posts method

Since Fabricator didn't work out of the box, I tried to use Rails fixtures. Basically, you create objects ahead of time in text files. Rails parses those and generates objects that you can use in your tests. The problem is that those are static - there's no good way to change something about them to fit the purposes of your test. I made a series of fixtures (valid/invalid, root/child `Posts` referencing topics) but it got obnoxious fast. Back to in-line object creation for now.