SecurityException when click Settings > Ringtone

If you click Settings > Ringtone a SecurityException is throwed (Nexus 5 - 4.4.2). This PR fix that.

I would push it directly but I don't know if you want to add permissions to the demo app.

```
12-27 14:16:56.224: E/AndroidRuntime(2745): FATAL EXCEPTION: main
12-27 14:16:56.224: E/AndroidRuntime(2745): Process: org.holoeverywhere.demo, PID: 2745
12-27 14:16:56.224: E/AndroidRuntime(2745): java.lang.SecurityException: Permission Denial: reading com.android.providers.media.MediaProvider uri content://media/external/audio/media from pid=2745, uid=10226 requires android.permission.READ_EXTERNAL_STORAGE, or grantUriPermission()
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.os.Parcel.readException(Parcel.java:1465)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:185)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:137)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.content.ContentProviderProxy.query(ContentProviderNative.java:413)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.content.ContentResolver.query(ContentResolver.java:461)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.content.ContentResolver.query(ContentResolver.java:404)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.media.RingtoneManager.query(RingtoneManager.java:556)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.media.RingtoneManager.getMediaRingtones(RingtoneManager.java:493)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.media.RingtoneManager.getCursor(RingtoneManager.java:366)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at org.holoeverywhere.preference._RingtonePickerDialog.create(_RingtonePickerDialog.java:108)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at org.holoeverywhere.preference._RingtonePickerDialog.makeDialog(_RingtonePickerDialog.java:148)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at org.holoeverywhere.preference.RingtonePreference.onCreateDialog(RingtonePreference.java:60)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at org.holoeverywhere.preference.DialogPreference.showDialog(DialogPreference.java:295)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at org.holoeverywhere.preference.DialogPreference.onClick(DialogPreference.java:188)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at org.holoeverywhere.preference.Preference.performClick(Preference.java:715)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at org.holoeverywhere.preference.PreferenceScreen.onItemClick(PreferenceScreen.java:119)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.widget.AdapterView.performItemClick(AdapterView.java:299)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.widget.AbsListView.performItemClick(AbsListView.java:1113)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at org.holoeverywhere.widget.ListView.performItemClick(ListView.java:635)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.widget.AbsListView$PerformClick.run(AbsListView.java:2904)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.widget.AbsListView$3.run(AbsListView.java:3638)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.os.Handler.handleCallback(Handler.java:733)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.os.Handler.dispatchMessage(Handler.java:95)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.os.Looper.loop(Looper.java:136)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at android.app.ActivityThread.main(ActivityThread.java:5017)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at java.lang.reflect.Method.invokeNative(Native Method)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at java.lang.reflect.Method.invoke(Method.java:515)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
12-27 14:16:56.224: E/AndroidRuntime(2745): 	at dalvik.system.NativeStart.main(Native Method)
```