Changed Flux Mining mechanics

Previously, Flux Mining would get unlocked at a specified level with a
specified chance. Once unlocked, the player would have no control over
this ability and some players complained they would like to be able to
turn it on and off.

By adding a new furnace recipe, to craft a special pickaxe - a Flux
Pickaxe - this issue is solved. If a player doesn’t want to use Flux
Mining, they simply shouldn’t mine using a Flux Pickaxe.

Crafting a Flux Pickaxe is simple, just place one of the vanilla
pickaxes in a furnace and cook it up.

Every time the ability is successful, extra durability damage is dealt
to the tool. Just like with other abilities.

Adds #2320