Add LoginReisterViewModel
Small changes to ViewModels
Change AppViewModel
Add user validation
Merge remote-tracking branch 'origin/master'

Conflicts:
	RecepiesClient/Data/DataPersister.cs
	RecepiesClient/Data/HttpRequester.cs
	RecepiesClient/Helpers/LoginSuccessArgs.cs
	RecepiesClient/Models/LoginResponseModel.cs
	RecepiesClient/Models/RecipeCreatedModel.cs
	RecepiesClient/Models/RecipeModel.cs
	RecepiesClient/Models/UserModel.cs
	RecepiesClient/RecepiesClient.csproj
	RecepiesClient/ViewModels/AppViewModel.cs
	RecepiesClient/ViewModels/IPageViewModel.cs
	RecepiesClient/ViewModels/ViewModelBase.cs