generate:form improvements (#14):

 * Add class crm-submit-buttons to button bars
 * Use translation with the text message
 * Output fields dynamically (FIXME: "Required" star is not rendered)
generate:form - Fix display of "required" fields (#14)
generate:form - Don't include textual boilerplate in tpl file
generate:form - Filter renderable field list in PHP instead of Smarty (#14)