Refactor source layout

Introduce compat source sets and move all kotlin sources to the main directory

[no changelog]

src/main/kotlin/gui/config/ManagedConfigElement.kt

@@ -0,0 +1,8 @@
+
+
+package moe.nea.firmament.gui.config
+
+abstract class ManagedConfigElement {
+    abstract val name: String
+
+}