Allow ModifyOrder() to change the LotSize

[Tantalus]

In order to use Pending Orders with a controlled risk strategy, the size of the order would need to be adjusted on a bar-by-bar basis until it was executed. This is not possible with the current version of ModifyOrder(). The alternative would be to delete and re-create each pending order every bar, so the new order would have a different LotSize than the previous one. That would be very inefficient.

Add one argument (LotSize) to the ModifyOrder() function and life would be much simpler.