Added a few ore dictionary Kegs.

Added some ore dictionary Kegs to store molten fluids (I've only
selected metals that have a higher melting temperature than 1300
degrees, due to that being the vanilla temperature of lava, and the
temperature of many molten fluids in the modding community.

I have also changed the Airtight Keg to the Slime-Sealed Keg, and have
added an IC2 compatible Rubber-Sealed Keg which can store gases,
similarly to the Slime-Sealed Keg.