Migrate gradle scripts to have multiple modules and source sets. Using Kotlin-DSL for enhanced script debugging.

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

core/build.gradle.kts

@@ -0,0 +1,15 @@
+
+plugins {
+    java
+}
+dependencies {
+    implementation("junit", "junit", "4.12")
+}
+val jar by tasks.getting(Jar::class) {
+    manifest {
+        attributes(mapOf(
+                "Implementation-Title" to project.name,
+                "Implementation-Version" to project.version
+        ))
+    }
+}

core/src/main/java/com/gmail/nossr50/McmmoCore.java

@@ -0,0 +1,5 @@
+package com.gmail.nossr50;
+
+public class McmmoCore {
+
+}