AwardCurrencyHandler returns String currencyName, int amount, String error
if function is successful , error is null
if function fails, currencyName & amount are null
EarnedCurrencyAlertHandler returns String currencyName, int amount, String error
In order to notify users that they’ve earned virtual currency since the last time the app queried the user’s currency balance,
if function is successful , error is null
if function fails, currencyName & amount are null
GetCurrencyBalanceHandler returns String currencyName, int amount, String error
if function is successful , error is null
if function fails, currencyName & amount are null
SpendCurrencyHandler returns String currencyName, int amount, String error
if function is successful , error is null
if function fails, currencyName & amount are null