Added permission nodes for each potion. All permission nodes are of the form splashcraft.use.[potion name in lower case] (for example, splashcraft.use.icy)
The default permission is "everyone" for all potions, except for Rusty and SuperConductive (see below)
If a player does not have permission to use a potion, they can throw it but nothing will happen.
Removed the recipe for the Rusty potion. It is now a non-craftable, admin only potion by default (you can add a recipe for it and change the permission setting if you like it to be available to players).
Added SuperConductive potion - Strikes the player/mob with lightning every 1 second for 10 seconds. This potion is non-craftable by default, and is not meant for PvP. Only admins have permission to use it by default.
