Convert ContentType to be an immutable data class
Convert some usages of String (for content type) to use ContentType
Do correct check for the text/css content type
Ensure that the UTF8ForTextAssets interceptor operates on the output of the CSSURLRewrite interceptor
Fix out-of-date message (WRO4J is not longer used)
Ensure correct ordering of interceptors
Perform lookup by ContentType mimeType (a String), not the ContentType itself