Add 'type' to OptionDefinition

[delner]

What does this PR do?

Adds a type field to OptionDefinition, which can be used to identify what kind of value the option should hold.

It also adds type to settings via to its OptionDefinition. type contains the auto-generated class used to encapsulate the option definitions contained within settings. Exposing this class allows you to metaprogram against an existing settings, such as adding or modifying option definitions.

Motivation

type allow for more descriptive option definitions, possibly type checking/coercion features later.

When creating settings options using the configuration DSL, it auto-generates an appropriate class with configuration behavior loaded. This class was entirely inaccessible, unless you instantiate the settings and its default value. Exposing type makes this class accessible without hacks.

Additional Notes

Also did a minor expansion on tests to encompass a bit more of the pre-existing behavior (adding coverage).