Improve config gui handling

src/main/kotlin/moe/nea/firmament/gui/WSplitPanel.kt

@@ -0,0 +1,23 @@
+package moe.nea.firmament.gui
+
+import io.github.cottonmc.cotton.gui.widget.WPanel
+import io.github.cottonmc.cotton.gui.widget.WPanelWithInsets
+import io.github.cottonmc.cotton.gui.widget.WWidget
+
+class WSplitPanel(val left: WWidget, val right: WWidget) : WPanelWithInsets() {
+    init {
+        left.parent = this
+        right.parent = this
+        children.add(left)
+        children.add(right)
+    }
+
+    override fun layout() {
+        expandToFit(left, insets)
+        expandToFit(right, insets)
+        (left as? WPanel)?.layout()
+        (right as? WPanel)?.layout()
+        left.setLocation(insets.left, insets.top)
+        right.setLocation(width - insets.right - right.width, insets.top)
+    }
+}