Add a couple of endpoints, one a stub, to be able to read topics
using the official client.

Many things work. Huzzah. Convo may also work now.
Get thread view working properly in the official tapatalk client

You can now browse by category and read any thread. Pagination is
a bit strange so I've not dealt with it yet - discourse goes by
page number, whereas tapatalk asks for ranges of posts - so that
needs fixing In The Future.

We're probably in a state to begin looking at push notifications now