Allow `clean` option to be specified with `extend`
Allow `clean` option to be specified with `extend`

Previously, `clean` could only be set when creating an instance of `ampersand-form-view`, not when extending the base view.
dhritzkiv/ampersand-form-view,AmpersandJS/ampersand-form-view,RickButler/ampersand-form-view,ahoym/ampersand-form-view