* model_details.html: using `Safe` filter

* server.config: `websites` Removed + new `allowed_hosts`

* DemoSettings.cs: `SITE_ID` Removed + new `ALLOWED_HOSTS`

* BadrHandler.cs:
* SiteSettings.cs:
    - Implementing `ALLOWED_HOSTS`

* BadrServer.cs: server can no longer host multiple sites.

* ServerSettings.cs: `Websites` Removed, replaced by single `Website`

* Utils.cs: New `Safe` filter

* ExprMatchGroups.cs: Ensuring that `Escape` filter is applied at the  end.

* VariableRenderer.cs: Taking account of the new `Safe` filter.