add profit loss description and moving average value

[mierin12]

Issue : https://forum.portfolio-performance.info/t/moving-average-ma-instead-of-first-in-first-out-fifo/19174
Hello,
This is a proposition to add

• A description to the Profit Loss column of the Statement of Assets
• The Profit/Loss for moving average method, and regroup both columns in a submenu

Before :

After :

I tried to reused some existing label. But maybe it is confusing to reuse the exact term "Unrealized Capital Gain" than in other column ? It is indeed an unrealized gain, only it is net and not gross in Profit/Loss.