T92 implement exchange rate class and conversion logic
T92 don't allow negative rates for ExchangeRates
T92 implement Yahoo Finance exchange rate provider
T92 Implement CurrencyConverter
T92 database persistence (work in progress)
T92 Improve test output
T92 Change test to use table
T92 Update query to return inverse rates
T92 Conversion javascript wip
Create Joda Money and CurrencyUnit binders
T92 - Add ajax calls to do conversion
T92 convert booking source amount on creation
T92 fix tests