Increment for BUY/SELL ORDER click

**Is your feature request related to a problem? Please describe.**
When filling the order book, I want to place my order slightly ahead of certain spots.
Now it depends on the rounding error, where my new order will be placed or I have to manually edit my sell/buy price.

**Describe the solution you'd like**
The BUY ORDER click should be multiplied by (1 + 10⁻5) for the input field number.
The SELL ORDER click should be multiplied by (1 - 10⁻5) for the input field number.

**Additional context**
This should also help to improve order book depth and spread.

No file, test, or entry point is named. Start by searching the repository for the BUY ORDER and SELL ORDER labels and their input fields, then trace the click behavior. Done means the requested multipliers are applied consistently and the order-book price and spread behavior is covered by an appropriate test.

Written by the indexing model from the issue text.