Trade Menu Functionality [Stage2/4]

[Greyrib]

• Staging of buy/sell items (FO4-style)
• Amount slider popup
• Identify whether items being staged belong to player or trader
• Too-early trade zone exit issue
• Interaction menu exit has to cancel any current staged trade

[Greyrib]

Rabbit hole with spending too many lines of code trying to count names pre- & post prelists & cargolists

[Greyrib]

• Staging for selling now functional

• Clearing no-item player-side trade buttons

• Returning/cancelling all sell-staged items triggers Unity-error (even on empty list)