Add support for `Slider<T>`

[tznind]

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

Fixes #274

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