Add MobEffect from mc-dev for diff visibility

Remapped by Srg2Source from Bukkit/CraftBukkit@df846d6ff84f6ad534f42ec03f3683122cec1752
Use wall time instead of ticks for several things. Fixes BUKKIT-4059

Currently furnace smelting and the item pickup delay timer use wall time
(aka actual time passed) to emulate a constant tick rate so run at the
same speed regardless of the server's actual tick rate. There are several
other places this makes sense so this commit converts them.

The item despawn timer is converted so now always takes 5 minutes. Users
know this 5 minute number well so keeping this constant helps to avoid
confusion. This also helps alleviate lag because if a large number of item
drops is the reason your server is running slowly having them stay around
longer just means your server is slow longer.

Potion brewing and the zombie villager conversion timer are now constant.
These match the furnace criteria of being useful for hiding lag and not
having a detrimental effect on gameplay.

Potion effects are now also using wall time. The client is told about effect
times in ticks and displays this information to the user as minutes and
seconds assuming a solid 20 ticks per second. The server does have
code for updating the client with the current time remaining to help
avoid skew due to differing tick rates but making this a constant makes
sense due to this display.

Remapped by Srg2Source from Bukkit/CraftBukkit@0c0899f0be12ef900ef45c5178a4ad81d6fed054
Merge in Forge's edits to PotionEffect now that CB edits it as well

Previously PotionEffect (CB name MobEffect) was added from the minecraft-forge
dependency, but now that its compiled in MCPC+ we need to add Forge's changes.

Required for MinecraftPortCentral/MCPC-Plus@a8720eea2f82e54b88a3eab33ca15e8b8d8cb47f