Render and sanitize chat messages server-side. (#237)

* Render and sanitize chat messages server-side. Closes #235

* Render content.md server-side and return it in the client config

* Remove showdown from web project

* Update api spec

* Move example user content file

build/javascript/package.json

@@ -10,7 +10,6 @@
     "@videojs/themes": "^1.0.0",
     "htm": "^3.0.4",
     "preact": "^10.5.3",
-    "showdown": "^1.9.1",
     "tailwindcss": "^1.8.10",
     "video.js": "^7.9.6"
   },
@@ -27,7 +26,6 @@
       "@justinribeiro/lite-youtube",
       "htm",
       "preact",
-      "showdown",
       "tailwindcss/dist/tailwind.min.css"
     ]
   },