Fixes #149 - Update Sample to use External ObservableCollection

[michael-hawker]

Fixes #149

We re-write the sample to use an external collection as a developer would in their app. This then properly lets the ItemsControl display just the tokenized items. (Though there's still an issue with how TokenizingTextBox behaves we should resolve.)

PR Type

What kind of change does this PR introduce?

• Sample app changes

What is the current behavior?

Trying to point to the ItemsSource of the TokenizingTextBox gives us the wrong collection.

What is the new behavior?

We use an external collection (as a developer would bind to their data model) and use that to bind to both the TTB and the ItemsControl. Then it works as intended.

Will open an issue on the main repo for tracking a fix to the underlying TTB.

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Sample in sample app has been added / updated (for bug fixes / features)
  • Icon has been created (if new sample) following the Thumbnail Style Guide and templates
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes

Other information

[ghost]

Thanks michael-hawker for opening a Pull Request! The reviewers will test the PR and highlight if there is any merge conflict or changes required. If the PR is approved we will proceed to merge the pull request 🙌