Make LocalePicker Fragment.

The logic calling selectFirst() is removed as
- There's no comment why it is needed.
- Actually SetupWizard gets stack as that forces users to see
  WirelessSettings in SetupWizard.

The other changes:
- Move back LocalePickerFragment to LocalePicker.
- Make <activity> for LocalePicker in AndroidManifest <activity-alias>
- Add a short comment about how getComponent(), which should be a key
  for understanding how top-level settings work.
- Modify LanguageSettings so that it corectly points LocalePicker as
  a fragment.

Change-Id: I78d356e40af896ba1aab72fba12c90467371c7b0

AndroidManifest.xml

@@ -225,14 +225,17 @@
             </intent-filter>
         </activity>
 
-        <activity android:name="LocalePicker" android:label="@string/language_picker_title">
+        <activity-alias android:name="LocalePicker"
+                        android:label="@string/language_picker_title"
+                        android:clearTaskOnLaunch="true"
+                        android:targetActivity="Settings">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <action android:name="android.settings.LOCALE_SETTINGS" />
                 <category android:name="android.intent.category.DEFAULT" />
                 <category android:name="android.intent.category.VOICE_LAUNCH" />
             </intent-filter>
-        </activity>
+        </activity-alias>
 
         <activity-alias android:name="LanguageSettings"
                 android:label="@string/language_keyboard_settings_title"