add Settings activity content

app/src/main/kotlin/com/simplemobiletools/thankyou/activities/SettingsActivity.kt

@@ -1,9 +1,28 @@
 package com.simplemobiletools.thankyou.activities
 
 import android.os.Bundle
+import android.support.v4.app.TaskStackBuilder
+import com.simplemobiletools.thankyou.R
+import kotlinx.android.synthetic.main.activity_settings.*
 
 class SettingsActivity : SimpleActivity() {
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
+        setContentView(R.layout.activity_settings)
+
+        setupDarkTheme()
+    }
+
+    private fun setupDarkTheme() {
+        settings_dark_theme.isChecked = mConfig.isDarkTheme
+        settings_dark_theme_holder.setOnClickListener {
+            settings_dark_theme.toggle()
+            mConfig.isDarkTheme = settings_dark_theme.isChecked
+            restartActivity()
+        }
+    }
+
+    private fun restartActivity() {
+        TaskStackBuilder.create(applicationContext).addNextIntentWithParentStack(intent).startActivities()
     }
 }