Remove fomantic accordion module (#15951)

Replace it with native <detail> element. Did some slight restyling on
the release downloads, new behaviour should be exactly the same
otherwise.

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

web_src/fomantic/semantic.json

@@ -21,7 +21,6 @@
   "rtl": false,
   "admin": false,
   "components": [
-    "accordion",
     "api",
     "breadcrumb",
     "button",