Explicitly set the request encoding to UTF-8 in a filter

There used to be a filter that set the request encoding in crowd, but it got removed a while ago (see CWD-2649) because it used to set the content-type as well.

The request encoding is now set by webworks, i.e. fairly low down the filter chain. That means that if any filter higher up the chain (such as OAuthFilter) tries to access the request parameters, they will be parsed using the default encoding (ISO-8859-1) instead of UTF-8.