Refactoring Purse Model to have more describtive function names, moved error checking to own method
Refactoring Purse model to be less currency specific and load currency type in as a dependecy
Adding Pound currency model, and refactoring Purse to make more generic calls to currency for config
Adding coin value method to pound to return the correct coin value for an amount of money

Changed Purse toCoinSet to use new coin definition interface from pound currecy