Handle / & /wiki & /wiki/ URLs

https://wikia-inc.atlassian.net/browse/HG-438
I don't like it neither but I assumed it's there for a reason.

@hakubo how about changing [this line](https://github.com/Wikia/mercury/blob/HG-438/server/controllers/article/index.ts#L55) to `data: payload`?

I don't know why we even have such grouping and duplication of data (`result.json` and `result.article` are the same data in different format) but it's probably just my ignorance.