Allow Splash Potions to be splashed like explosions and lightning. Fixes BUKKIT-2542

JIRA ticket: https://bukkit.atlassian.net/browse/BUKKIT-2542

Should allow spawnable potions.

Potion p = someWorld.spawn(to, Potion.class);
p.setSplash(true); // Required for splash potions.

**Side note:** lines 17, 21 and 29 contain redundant imports.