FIX: Support ember app routing to topics with only slugs
SECURITY: Stripping links could unescape html fragments
Revert "FEATURE: fenced code blocks can hint with "pre" or "text""

This reverts commit 943ad8d1d54cc39f297198c338d484d98a4e7536.
FIX: When emoji was disabled you could get a JS error in preview
FIX: update user preferences was failing if custom_fields is blank string