Add framework to develop model-based pages

[Kaliumhexacyanoferrat]

As a developer, I would like to add web pages with additional logic in their model classes, so that I can handle situations like submitted data.

Example

var page = Page.Create<SomeModel>(ScribanView.From("someview.html"));

public class SomeModel : PageModel
{
  public string MyProperty { get; }

  public void OnPost() 
  {
    // ...
  }
}

Acceptance criteria

• The framework is available as a separate nuget package
• The framework allows to work with views from different rendering engines (e.g. #48)
• There is an additional router which allows to specify a whole directory with view files
• The framework aligns with Razor Pages where appropriate to keep the learning curve low