Show price quotes in preferred currency for every trading pair

From Luke Stokes via Facebook:

>Luke Stokes I'd love to see a way to display prices in USD terms. Maybe with a mouse over? It's hard to know if 29,222.86996 BTS per BTC is a good price.

>Calvin Froedge Show prices in BITUSD. Go to settings and change your "Preferred Unit of Account" to USD.

>Luke Stokes I already have that turned on. I mean on the actual trading pairs. Like if I'm looking at the BTS/BTC exchange, and I see a rate of 29,222.86996 BTS per BTC, I have to then go to my spreadsheet and figure out what that means in terms of USD. A mouse over of the individual buy/sell prices in USD terms (or preferred currency terms) would be _so_ helpful.

This would mean that when buying / selling asset pairs, or even looking at the order book, we would be able to see things in terms of our preferred unit of account. Perhaps another column or a hover.

No source files or tests are identified. Start with the trading-pair buy/sell views, order book, and the preferred unit of account setting; determine how USD or the selected preferred currency can be shown for each quote. Done means every trading pair exposes quote values in the preferred currency without requiring manual conversion.

Written by the indexing model from the issue text.