On a dirt path that passes for a street in a Kenyan refugee camp, a merchant sells grains he bought from a local farmer outside the settlement. To call it an “economy” would be euphemistic, but it’s a living, and it’s enough to support his wife and two children — a family he’s built since arriving at the camp over a decade ago. [...] Mastercard and Western Union have spent the past year studying the needs of these international camps-turned-cities.