Improve price step during create offer (applies to buy direction)

[axpoems]

As follow-up from #1949:

• [ ] Make offer price recommendation.
• [ ] Use colours to give the feedback: red/orange/green.
• [x] Add amount step before price, then this info can be used to adjust the recommended ranges and price recommendation.

[HenrikJannsen]

Can that issue be closed?

[axpoems]

I intend to work on it, don't close it.