Refactor Hooodoo exception reporting to a "first-class" module (Trello import)

[pond]

Make this a first-class module which can be used in its own right, rather than something embedded into the middleware.

Technically it can be used on its own, but the namespacing is weird. It'd break Guides links and the like to move it completely, so this would be fiddly. It could be OK just to leave it as-is, but it's messy.

[Andrew Hodgkinson]