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!

android/src/main/kotlin/ch/dissem/android/MainActivity.kt

@@ -0,0 +1,24 @@
+package ch.dissem.android
+
+import android.os.Bundle
+import androidx.activity.ComponentActivity
+import androidx.activity.compose.setContent
+import androidx.compose.runtime.Composable
+import ch.dissem.yaep.ui.common.App
+import org.jetbrains.compose.ui.tooling.preview.Preview
+
+class MainActivity : ComponentActivity() {
+    override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+
+        setContent {
+            App()
+        }
+    }
+}
+
+@Preview
+@Composable
+fun AppAndroidPreview() {
+    App()
+}