WPF .NET 5 getting started article will need to demonstrate more

[adegeo]

Related to #60

After the revamp of the .NET 5 WPF content is published, there will be a new getting started article that creates a new app. This app is pretty simple compared to the .NET Framework walkthrough. This article should be expanded into multiple articles that build on the previous one and introduce new concepts.

1. Part 1

   This is the basic article that will be published. Currently it's here.

   • Creating an app in Visual Studio
   • Create some basic controls
   • Respond to button click to add names to controls

2. Part 2

   Dives into {binding} the UI with some backend data (all in app).

   • Creating an ObservableCollection for the names list
   • Change the button to add names to the collection
   • Bind the collection to the ListBox
   • Expand the data types to a full address book record instead of just name
   • Introduce a Delete button to remove an item

3. Part 3

   Explore validation on input

   • Expand UI to support all fields of the address book
   • Add "favorite" field
   • Expand UI to support toggling "favorite"
   • Add validation to data entry controls.
   • Toggle Add button based on if record is valid.

4. Part 4

   Explore the styles and themes features of WPF.

   • Add a DataTemplate to the ListBox.
   • Add multiple DataTemplate to the ListBox based on "favorite".
   • Adjust validation styles.
   • ???

5. Part 5

   ???