Restore component helpers

[daftspunk]

There are several requests to bring back the component API from v1 in this plugin, alongside the new approach of using Twig logic.

We should implement this as v2.1 feature release.

References:

• https://talk.octobercms.com/t/user-plugin-3-x-ajax-login-no-redirect/2815/3
• cant restrict the user on page by group #563
• Missing Sign in requires activation #555