Add ability to modify ThrownPotion properties. Adds BUKKIT-3197

Remapped by Srg2Source from Bukkit/CraftBukkit@fbfbc316627c4b36d7d621e199a9550e67496a12
Stationary lava is also a LAVA ignition cause.

Remapped by Srg2Source from Bukkit/CraftBukkit@7e17c4ed786b81c6e7eac2b3e981fed36c36741c
Add BlockDropper for diff visibility

Remapped by Srg2Source from Bukkit/CraftBukkit@614e51857725ce93ddc24644349ca5b5fbf17186
Implement Dropper interface. Adds BUKKIT-3750

Remapped by Srg2Source from Bukkit/CraftBukkit@e869277070a51863ecc2c94ea02298af534fa0a0