Fuel Exchange Improvements

[vernal sparrow]

1. Show the top rail price.
2. Show the discount before purchasing.
3. Show the net total fuel after discount.
4. Change "discount" display to "market price" display.
5. Show discount chart
6. Show price history chart.
7. Use buy order book instead of just filling sell orders.
8. Show sell order book.
9. Show lowest fuel price instead average price.

Please add what you want to improve and I will update the list.

[last frigate]

Sending fuel to a friend.