Feature 6082

Feature: https://github.com/OpenRA/OpenRA/issues/6082
Regression tested - From what I can see no bugs or performance issues.

Order.cs : Line 241: 
- Function ClearProduction() inputs new order to the ProductionQueue

ProductionQueue.cs: Line 323: 
- Case statement "ClearProduction" counts number of items paused for item
- Deletes all paused items for that icon and returns appropriate fees if applicable

ProductionPaletteWidget.cs: HandleKeyPress(KeyInput e) && bool HandleEvent(ProductionIcon icon, bool isLeftClick)
- Former to remember Control is key up or down with bool (hold/release)
- Latter to call new production order "ClearProduction" for item LCtrl + Click on