@action
  schemaUpdated() {
    let oldSchema = this.oldSchema;
    let newSchema = this.schema;
    if (newSchema && newSchema !== oldSchema) {
      // eslint-disable-next-line ember/no-runloop
      scheduleOnce('actions', this, this.setupColumns);
    }
    this.oldSchema = newSchema;
  }
Hook called whenever attributes are updated.
We use this to listen to changes to the schema.
If the schema changes for an existing `list` component
(happens when switching model types for example), we need
to rebuild the columns from scratch.

@method schemaUpdated
@param  {Object} newAttrs and oldAttrs