Added LED color customization option

- ColorPickerView.java: based upon "HoloColorPicker" which is Open
Source
- ColorPickerDialog.java: a dialog which wraps ColorPickerView
- Added options in SettingsNotificationsActivity
- Now MessagesController gets the led ARGB color from SharedPreferences
(Keys: "NotificationLEDColor" and "NotificationGroupLEDColor")