More improvements on CrossPlatformSettingsProvider
* Fix bug related to missing folder location
* Add documentation for future class users

--HG--
branch : FlexBridgeAlpha
More improvements after trying to use CrossPlatformSettingsProvider on mono
* Eliminate code that isn't needed when specifying the Provider in the designer
* Changed notes to indicate the preference of defining the Provider in the
  designer.
* Change the test app to use settings in the new way

--HG--
branch : FlexBridgeAlpha