trade: add pool constructor options

[yerden]

Changes:

• downgrade OrderPool to interface;
• add OrderPoolMatcher class;
• introduce OrderMatcher optional parameter for TradingPool and HistoryPool constructors.

These changes don't violate current API and allow to reduce boilerplate code in case of defining TradingPool and HistoryPool since matching criteria for both are often identical. It can also be useful when defining pools as RAII objects. For example:

class MagicAndBuyMatcher: public OrderMatcher
  {
private:
   int               m_magic;
public:
                     MagicAndBuyMatcher(int m):m_magic(m){}
   virtual bool      matches() const {return Order::MagicNumber()==m_magic && Order::Type()==OP_BUY;}
  };
...
// elsewhere
   MagicAndBuyMatcher myMatcher(1337);
   TradingPool tp(&myMatcher);
   HistoryPool hp(&myMatcher);
   foreachorder(tp) {
   ...
   }