Restructure project

* use modules instead of source sets
* Kotlin JVM instead of multiplatform (for now) to make things simpler
* Warning: GameCell doesn't use mutableState anymore, this needs to be
           fixed for the UI to work!

desktop/proguard-rules.pro

@@ -0,0 +1,25 @@
+-libraryjars  <java.home>/jmods/java.base.jmod(!**.jar;!module-info.class)
+
+-keepclasseswithmembers public class MainKt {
+    public static void main(java.lang.String[]);
+}
+
+-dontwarn kotlinx.coroutines.debug.*
+-dontwarn kotlinx.datetime.**
+
+-keep class kotlin.** { *; }
+-keep class kotlinx.coroutines.** { *; }
+-keep class org.jetbrains.skia.** { *; }
+-keep class org.jetbrains.skiko.** { *; }
+
+-ignorewarnings
+
+# Windows folders
+-keep class com.sun.jna.* { *; }
+-keepclassmembers class * extends com.sun.jna.* { public *; }
+
+-assumenosideeffects public class androidx.compose.runtime.ComposerKt {
+    void sourceInformation(androidx.compose.runtime.Composer,java.lang.String);
+    void sourceInformationMarkerStart(androidx.compose.runtime.Composer,int,java.lang.String);
+    void sourceInformationMarkerEnd(androidx.compose.runtime.Composer);
+}