convert SimpleActivity to kotlin

app/src/main/kotlin/com/simplemobiletools/notes/activities/SimpleActivity.kt

@@ -0,0 +1,28 @@
+package com.simplemobiletools.notes.activities
+
+import android.os.Bundle
+import android.support.v7.app.AppCompatActivity
+import android.view.MenuItem
+
+import com.simplemobiletools.notes.Config
+import com.simplemobiletools.notes.R
+
+open class SimpleActivity : AppCompatActivity() {
+    lateinit var config: Config
+
+    override fun onCreate(savedInstanceState: Bundle?) {
+        config = Config.newInstance(applicationContext)
+        setTheme(if (config.isDarkTheme) R.style.AppTheme_Dark else R.style.AppTheme)
+        super.onCreate(savedInstanceState)
+    }
+
+    override fun onOptionsItemSelected(item: MenuItem): Boolean {
+        return when (item.itemId) {
+            android.R.id.home -> {
+                finish()
+                true
+            }
+            else -> super.onOptionsItemSelected(item)
+        }
+    }
+}