Add option for node can limit price

[thanhson1085]

TomoX protocol allow user can place order with any price.

It will be an issue spammers want to create spam order to attack chaindata.

So I propose that we should have a option for node can limit order price.

e.g: If node is running with with --pricelimit 100, then user can not place order with price > current_price + 100 * current_price