Makes SpongePowered support Bukkit plugins (that doesn't requires net.minecraft.server and org.bukkit.craftbukkit packages from the old CraftBukkit)

First, be sure to initialize the Git submodules:

git submodule update --init --recursive

Now, use maven to build the bukkit module:

cd bukkit
mvn clean install
cd ..

Then use the provided Gradle runtime to compile:

./gradlew build

NOTE: YOU MAY NEED TO INSTALL THE LATEST SpongePowered AND MinecraftForge INTO YOUR LOCAL MAVEN REPOSITORY.