Add link to external SSO profile to profile page

[cpradio]

PR Submitted (ping @nec286)

DEV: Add plugin-outlet to allow SSO sites to put a message on the User Preferences page

@pfaffman, you would use this #howto to implement it via a site customization (also see example below)

Adding to plugin-outlets using a theme

In Plugin System Upgrades @eviltrout introduced a system for extending Discourse HTML using plugin outlets. Plugin outlets are tagged areas in our application that allow you to inject a template. The template has access to the backing controller so it can be dynamic. Our theme system in /admin/customize/themes allows you to define custom CSS and HTML. When injecting HTML into your page you can also inject templates, this gives you a very simple mechanism for injecting content into various plu…

<script type='text/x-handlebars' data-template-name='/connectors/above-user-preferences/sso_notice'>
{{#if siteSettings.enable_sso}}
  modified contents of connectors/above-user-preferences/sso_notice.hbs file goes here
{{/if}}
</script>