Merge commit from fork

* Rework frontend code interacting directly with DOM

Rework frontend code that uses user-supplied data to render things like
comments and notes. In places where using React's built-in sanitization
is possible, the feature is used. In other places, where some markup
might be necessary, DOMPurify is used to sanitize the HTML before
rendering it.

Solves: GHSA-rh3r-8pxm-hg4w

* Remove test post DOM rework

* fixup! Rework frontend code interacting directly with DOM

ui/src/layout/Login.jsx

@@ -136,6 +136,8 @@ const FormLogin = ({ loading, handleSubmit, validate }) => {
               {config.welcomeMessage && (
                 <div
                   className={classes.welcome}
+                  // Use dangerouslySetInnerHTML to allow admins to configure
+                  // whatever content they want
                   dangerouslySetInnerHTML={{ __html: config.welcomeMessage }}
                 />
               )}