"Required" entity loading in HTTP mechanics

[jeremydmiller]

See this conversation:

https://hachyderm.io/@[email protected]/110695794643161320

The general idea is to do something that eliminates this whole usage of IResult. You frequently run into HTTP endpoints where you want to first load a related entity, then map it somehow to the response. If the entity does not exist, the route should stop and return a 404.