WorldBorder and Potions

Added new method to set the startingDiameter, endDiameter and the time it will take [void setDiameter(double startDiameter, double endDiameter, long time);]
Added Splash potion option.
Changed Radius to Diameter.
Changed get/setBlockBuffer to get/setBuffer and changed the return and parameter to double as it is not measured in whole blocks.
I strongly disagree. If I'm creating a PotionEffect, I don't care whether it's a "splash" potion or not. All I care about is the Effect the PotionEffect describes. To be frank, "Splash" is still not within the focus of a PotionEffect, it still belongs well within the realm of a PotionItem of sorts. So no.

If you wish to continue this discussion, I strongly suggest you split this PR into two as I've stated in the PR itself multiple times now.