* DEV: Sanitize HTML admin inputs
This PR adds on-save HTML sanitization for:
Client site settings
translation overrides
badges descriptions
user fields descriptions
I used Rails's SafeListSanitizer, which [accepts the following HTML tags and attributes](018cf54073/lib/rails/html/sanitizer.rb (L108))
* Make sure that the sanitization logic doesn't corrupt settings with special characters
Roman Rizzi