Change Xeiam Ticker Volume to reflect the base currency volume.

This change will unify the currency that the ticker volume is quoted in for all exchanges.  I confirmed with exchanges that only report a single volume (kraken, bitstamp, justcoin, vault of satoshi and btcchina) that they all report their volume using the base asset.  I'm still unsure about bitfinex, but I have sent them an email to confirm.