Add ability to set default character encoding on a subsystem level

Stuart: the charset one should be pretty simple, just an attribute on <servlet-container?
Stuart: ideally we would also have it in jboss-web.xml as well
Stuart: I should also add an option to use the connector encoding
Stuart: as connectors have their own encoding set
Stuart: that is used to decode the URL
Stuart: we should have an option to use the connector encoding as the default encoding