Add "Add custom rule to show clipboard item" functionality

[Apollys]

If a user wanted to quickly show a specific item (for example, suppose they've set lowest visible oil to Crimson but want to see Violet specifically), user should be able to Ctrl-C the item and click a button, which would then add a custom Show rule to .rules, based on:

• BaseType
• Class (maybe redundant)
• Rarity, if present