Allow inverse input for Quantity/Total scaled orders

**Describe the bug**
The buying asset **Quantity** field and the buying asset **Total** field should have the inverted unit to fit the selling side.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to Exchange Scaled orders
2. Compare fields with portfolio unit

**Expected behavior**
Use portfolio unit for order amount and the other unit for calculation of Total field.
Buy Quantity field in BTS (input) and Buy Total field in bitUSD (output).

**Screenshots**

Start at the Exchange Scaled orders interface and compare the buying asset Quantity and Total fields with the portfolio unit behavior described in the issue. Done means the buy Quantity input uses BTS while the buy Total output uses bitUSD, with the inverse unit used for calculation.

Written by the indexing model from the issue text.