Add support for Slider<T>

[tznind]

Adds support for creating <T> views e.g. Slider<int> or TreeView<MyGameObject>

Fixes #274

• Add a Slider<T> to view
  • Prompt user to pick a Type for T when adding a Slider<T>
  • Create the corresponding T Type
  • Restrict to value types only
• CodeDOM
  • Construct and add private field instance for Slider<T>
  • Populate Property Options
• Design Options property
  • Support for List<T> with complex type (i.e. SliderOption<T>)
  • Array Editor for complex types
  • Editor for SliderOption<T>