Implement undo functionality

Not quite sure about its usability though

commonUI/src/commonMain/kotlin/ch/dissem/yaep/ui/common/App.kt

@@ -127,10 +127,8 @@ fun PuzzleGrid(
                         allOptions.map { Toggleable(it, item.options.contains(it)) }
                     }
                     LaunchedEffect(item) {
-                        item.optionsRemovedListeners.add { removed ->
-                            options
-                                .filter { removed.contains(it.item) }
-                                .forEach { it.enabled = false }
+                        item.optionsChangedListeners.add { enabled ->
+                            options.forEach { it.enabled = enabled.contains(it.item) }
                         }
                         item.selectionChangedListeners.add {
                             selection = it
@@ -151,9 +149,17 @@ fun PuzzleGrid(
                         },
                         selectedItem = selection,
                         onSelectItem = {
-                            item.selection = it
                             if (it != null) {
+                                grid.snapshot()
+                                item.selection = it
                                 row.cleanupOptions()
+                            } else {
+                                while (item.selection != null) {
+                                    if (!grid.undo()) break
+                                }
+                                options.forEach {
+                                    it.enabled = item.options.contains(it.item)
+                                }
                             }
                         }
                     )