Simple example: Sync schema, uiSchema and formData

[jorisw]

Syncs schema, uiSchema and formData for the Simple example in the playground

Reasons for making this change

This example was a mess, while it's the first example your first time users will ever see.

It makes no sense to have properties commented out in form schema, or to have uiSchema entries for which no schema properties exist.

Uncomments some of the schema properties that were present in the uiSchema, and adds missing formData.

Checklist

• [x] I'm adding or updating code
  • [x] I've updated docs if needed

[jorisw]

Done