added open_exchange_rates_provide
initial tests on OpenExchangeRates passing
finish api testing
Merge remote-tracking branch 'origin/exchange_controller' into exchange-converter
begin exchange tests
Merge branch 'openexchangerates_api_learning' into exchange-converter
implemented OpenExchangeRates gem for talking to API
Merge remote-tracking branch 'origin/exchange-converter' into develop

Conflicts:
	app/controllers/exchanges_controller.rb
	app/models/exchange.rb
	spec/controllers/exchanges_controller_spec.rb
	spec/models/exchange_spec.rb