OPTIONS support - Gracefully ignore not supported controller actions

I'll push tests in a bit.

Is there a way to expose routes?
something like

```js
/**
 * OPTIONS /resource
 */

module.exports.options = function *options() {
  this.status = 200
  // this.header['Allow'] = 'GET,POST,PUT,DELETE,OPTIONS']
  this.set('Access-Control-Allow-Origin', '*')
  this.set('Access-Control-Allow-Methods', 'POST, GET, PUT, DELETE, OPTIONS')
  this.set('Access-Control-Allow-Credentials', false)
  this.set('Access-Control-Max-Age', '86400') // 24 hours
  this.set('Access-Control-Allow-Headers', 'X-Requested-With, X-HTTP-Method-Override, Content-Type, Accept')
     
  this.body = this.app.router.routes.describe('resource')
}
```

If not we should work on that