[ExchangeRateManagement WIP] Added currency selection activity.
[ExchangeRateManagement WIP] Added currency selection activity interaction. Controller refactoring.
[ExchangeRateManagement WIP] Restructured currency selection and amended test accordingly, introduced callback for I18N, replaces currency selection spinners by buttons, removed currency selection spinner callbacks.
[ExchangeRateManagement WIP] Corrected one remaining currency selection test, added delete Database to other exchange rate persistence tests.
[ExchangeRateManagement WIP] Added auto-saving of rates.