feat(comments): add https://cactus.chat support (#298)

* feat: Add https://cactus.chat as comments provider

* Add cactus comments config fields to exampleSite

* Add cactus css and js to external.yaml and move custom cactus css to html

* Remove unneeded cactus comments css

* Load external dependencies for cactus comments in the comments provider

* Use safeJS instead of safeHTML

data/external.yaml

@@ -36,3 +36,12 @@ KaTeX:
       integrity: sha384-vZTG03m+2yp6N6BNi5iM4rW4oIwk5DfcNdFfxkk9ZWpDriOkXX8voJBFrAO7MpVl
       type: script
       defer: true
+
+Cactus:
+    - src: https://latest.cactus.chat/cactus.js
+      integrity:
+      type: script
+      defer: false
+    - src: https://latest.cactus.chat/style.css
+      integrity:
+      type: style