Properties should have their own Editor

Summary: For the time being, to edit a Property, you have to use the old Advanced Editor. That works, but it sucks. We should instead have a consistent Property Wizard, built from the current Create a Property pane in the Edit page.

As part of this epic, we should also make the meta-Property system much more powerful, so that the Property Editor can be entirely data-driven, offering you the meta-Properties that are useful to this Type. This implies that a Type can declare the meta-Properties that are appropriate to it. We should also have a way to declare that a meta-Property is "general", applicable to all Properties, and make those easy to add. (For instance, Edit Width.)

Also, leave some room to define Wizards in here. For example, we should have a pseudo-Type named "Choice"; when you choose that, the rest of the Property Wizard shows the Choice Wizard, which wraps up the complexity of building a Choice. This one needs to be very powerful, and includes, eg, creating the backing Model and its Instances if desired.