New Currency and CurrencyPair

Added Dogecoin Currency/CurrencyPair.
DOGE -> XDC in BTER
DOGE -> XDC in Currencies
DOGE -> XDC in CurrencyPairs
DOGE -> XDC in Vircurex
Added XDC to MoneyDataExtension
Merge pull request #317 from dhenry/develop

New Currency and CurrencyPair