UI - make engine list more consistent with the auth method list (#4598)

* remove expanding behavior from engines list and add a configuration route

* use page header component, secret tab component for the template on the secret engine configuration route

* move abstraction to secret-list-header and remove secret-tabs

* add attrs to secret engine model and adjust mount controller code to support that

* fix top level nav so that we can use the back button properly

* fix tests

ui/app/router.js

@@ -68,6 +68,7 @@ Router.map(function() {
         this.route('backends', { path: '/' });
         this.route('backend', { path: '/:backend' }, function() {
           this.route('index', { path: '/' });
+          this.route('configuration');
           // because globs / params can't be empty,
           // we have to special-case ids of '' with thier own routes
           this.route('list-root', { path: '/list/' });