Split up dependencies for multiple version support.

The "core" module will house the entire abstraction layer of mcMMO, while
the "bukkit" and "sponge" modules will house common code to share between
the various versions being supported for each platform. Specifically,
spigot will be split up based on the listener handlers being registered,
and will be shadow packaged according to their targeted Minecraft version.
Sponge's multi-version dependency will be based on the API version, since
the only constant known between the various API versions is the plugin
annotations and basic listener annotations.

Signed-off-by: Gabriel Harris-Rouquette <gabizou@me.com>

bukkit/1_8_8/build.gradle.kts

@@ -0,0 +1,10 @@
+
+plugins {
+    java
+}
+
+dependencies {
+    implementation("org.spigotmc:spigot-api:1.8.8-R0.1-SNAPSHOT") // Spigot API
+    implementation("com.sk89q.worldguard:worldguard-legacy:6.1.2") // Old worldguard
+
+}