Introduce MarketMetadata

My attempt to resolve #379 

provides minimum price, trade and scales for currency. Values missing from the exchange API are read from a properties file.
MarketMetadata allows validating orders against the above and exchange specific limitations, like min and max price.

Also provides fee percent, though there is already a method for this but it doesn't accept CurrencyPair.
I'm not sure what to do with this, I was thinking about making the AccountInfo.tradingFee a Map<CurrencyPair, BigDecimal>.
what is this for?