Admin: Create a demo adapter

[eirikurn]

We need a demo adapter to better demonstrate the functionality of Tux Admin in tux-example-site.

The adapter should have a simple way to initialise data. Something like this:

import { define } from 'tux-adapter-localstorage'
import { registerEditable, MarkdownField, Input } from 'tux'

// interface Instance {
//   id: string
// }
// function define<T extends Instance>(model: string, instance: T): void

registerEditable('Quote', [
  {
    field: 'quote',
    label: 'Quote',
    component: MarkdownField,
  }
  {
    field: 'author',
    label: 'Author',
    component: Input,
  }
])


define('Quote', {
  id: 'foo',
  quote: '50% of the time, it works 100%',
  author: 'Eirikur',
})

// [snip]

import { Adapter } from 'tux-adapter-localstorage'
import { tuxMiddleware } from 'tux'
createChain()
  .chain(tuxMiddleware({
    adapter: new Adapter()
  }))

The define method should only save the instance if one doesn't already exist with the same id. It should only perform soft-deletes (so instances aren't recreated when you refresh).

The adapter's query api should be able to query in instance by id and type.