added the StorageService and refactored the SettingsViewModel so it will use it

Added the ObjectStorageHelper as a nuget package
removed the ServiceUrl property of the SubsonicServiceConfiguration in favor of an extension method which uses the base url property
renamed the NotificationManager to NotificationService and modified the way notifications are shown so that they will play a sound only if the user chooses to do so from the Settings page Related to #51
updated the PlaybackViewModel so that it can handle add Album,Artist or MusicDirectory items Related to #43
made some minor modifications to the audio layout to fit to smaller screens
fixed a logic bug where the type of the Artist class should actually be MusicDirectory
update the readme to show a usefull hint
did some minor refactorings
added the delete method to the StorageService
fixed failing test
added the WinRTWrapperService and moved some code from the App class to ShellViewModel
updated the ServiceResultBase class so that it will automatically execute a MessageDialogResult in case of an error and also updated the way it executed HttpClient requests to actually catch exceptions (previously they where not catched due the fact the method chain between the try-catch statement and the actual call contained an async void method - a known bug? in WinRT)

http://social.msdn.microsoft.com/Forums/en-US/winappswithcsharp/thread/bea154b0-08b0-4fdc-be31-058d9f5d1c4e
Merge branch 'master' of github.com:Agilefreaks/SubSonic8
Merge pull request #13 from cristi-badila/master

Refactorings and error handling