Coins, ores, slag now recyclable.
Objects now melt() into slag if their melt_temperature is set.
Define melting points.
Merge branch 'Bleeding-Edge' of github.com:d3athrow/vgstation13 into melting

Conflicts:
	code/game/objects/items/stacks/sheets/glass.dm
	code/game/objects/items/stacks/sheets/mineral.dm
	code/setup.dm
Merge pull request #1832 from N3X15/melting

Slag