Allow to make other (non .adp) kinds of resources "theme aware" and use this to provide a theme mapping to the /resources/ URL pattern, then use this new capability to allow the override of css in the chat implementations
Give xowiki chat also some kind of nice skin and centralize css retrieval
TODO: something smarter can be done in order to retrieve the proper css, based e.g. on theme, chat skin (to be implemented) etc. To be discussed is some way to resolve resources based on the theme.