Adds some metal variants to vanilla items

Items with variants:
- Big Bolt - Gold, silver, bronze
- Cash Register - Gold, silver, bronze
- Cookie Mold Pan - Gold, silver, bronze
- Egg Beater - Gold, silver, bronze
- Gold Bar - Silver, bronze
- Golden Cup - Gold, silver, bronze
- Garbage Lid - Gold
- Jar of Pickles - Gold
- Large Axle - Gold, silver, bronze
- Metal Sheet - Gold, silver, bronze
- Pro-Flashlight - Gold
- V-Type Engine - Gold, silver, bronze
- Gift Box - Gold, silver, bronze
All items are conductive. Some silver items look very close to their default counterparts, might be dealt with later. Also more items added later maybe
Formulas I made up for balancing the default weights
As of 0.0.6, these formulas are not exact but still used as a general guideline
Bronze
- Weight = Original weight+15%
- Value = Original value+40%
- Rarity = Averaged original rarity weight across all moons/3
Silver
- Weight = Original weight+30%
- Value = Original value+80%
- Rarity = Averaged original rarity weight across all moons/5
Gold
- Weight = Original weight+45%
- Value = Original value+120%
- Rarity = Averaged original rarity weight across all moons/7
Credits