Renewable Obsidian from Cauldrons

This is a minor change that would help with expanding the pre-diamond phase, which seems to be intended with the new copper tools.

As there are naturally generated portals in the world (and other tricks like using buckets), diamonds are not needed to reach the Nether. To make this process easier, I suggest adding an interaction where Water is placed into a Cauldron with Lava already in it, resulting in Obsidian forming. Right-clicking the Cauldron would remove the Obsidian. Rain could potentially cause this interaction as well. This would allow players to build portals close to home should they choose to risk entering the Nether early.

This feature could be balanced by adding a "cooling time" before formation, similar to the long time to mine currently present. Also, this would open the door to semi-automatic Obsidian production through use of either a Piston double extender or two Dispensers, a Redstone clock, and the Dripstone mechanics currently present in game. 

Thank you for reading.