Make a few small tweaks/suggestions

- Switch from Net::HTTP to Faraday
- Add `find_bet` before action to BetStepsController
- Swap `class << self` for preferred `def self.methodname`
- Better error definition in BetsController
I think it should be a class method in the `User` model because it deals with the finding or creating of a `User` object. I can't really think of anywhere else this DSL should be. Just my initial thought.