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!

build.gradle.kts

@@ -1,9 +1,18 @@
+import org.jetbrains.kotlin.gradle.dsl.JvmTarget
+import org.jetbrains.kotlin.gradle.tasks.KotlinJvmCompile
+
 plugins {
     // this is necessary to avoid the plugins to be loaded multiple times
     // in each subproject's classloader
     alias(libs.plugins.androidApplication) apply false
     alias(libs.plugins.androidLibrary) apply false
     alias(libs.plugins.jetbrainsCompose) apply false
-    alias(libs.plugins.kotlinMultiplatform) apply false
-    alias(libs.plugins.jetbrainsKotlinJvm) apply false
-}
+    alias(libs.plugins.kotlin.multiplatform) apply false
+    alias(libs.plugins.kotlin.jvm) apply false
+}
+
+tasks.withType<KotlinJvmCompile>().configureEach {
+    compilerOptions {
+        jvmTarget.set(JvmTarget.JVM_11)
+    }
+}