Fix maxSpeed not working for boats. Fixes BUKKIT-4242

When CraftBukkit updated to 1.3.1 with commit ea5109cc39, changes made to how boats worked broke this functionality. This restores that functionality and also changes the maxSpeed to match what is now used in vanilla, which is .35D instead of .40D
Implement get/set damage method for boats. Adds BUKKIT-5325

This brings the same functionality to boats that currently exists only for minecarts.
Deprecate occupiedDeceleration

Due to changes in how Minecraft handles boats, this value is no longer
constant, but instead dynamically calculated based on other variables.