Various improvements to packaging

This fixes several issues I had with consuming multi-loader CC:T in
various upstream mods.

 - Include /all/ sources in the Forge/Fabric jar. Before it was just the
   common classes, and not the core or API.

 - Use some Gradle magic to remove superfluous dependencies from the POM
   file. Also make sure Cobalt and Netty are present as dependencies.

 - Start using minimize() in our shadow jar config again.

buildSrc/src/main/kotlin/cc/tweaked/gradle/XmlUtil.kt

@@ -0,0 +1,12 @@
+package cc.tweaked.gradle
+
+import groovy.util.Node
+import groovy.util.NodeList
+
+object XmlUtil {
+    fun findChild(node: Node, name: String): Node? = when (val child = node.get(name)) {
+        is Node -> child
+        is NodeList -> child.singleOrNull() as Node?
+        else -> null
+    }
+}