Add avg rate for every market order trx

For market transactions such as limit_order_create or fill_order, it would be useful to add, under the visualized data view, wording stating the avg at which the transaction was set or executed, for example:

"...for at least 35.479 HBD " add "at an avg rate of 0.19 HIVE/HBD"

The value is calculated by dividing the amount of HIVE by HBD under the transaction (or planned amount).