Local system default preferences for all Jalview users on a system

If the user doesn't have a preferences file, then Jalview should look in a default preferences location like /etc/jalview_preferences to pick up any local system defaults like JABAWS server URLs, DAS registries, etc.

If the user subsequently customises any settings, then those settings should be written to the users own properties file. In principle, when a local system proprties file exists, only a minimum set could be written in the user's own directory, rather than the full properties dump that Jalview 2 creates, allowing admins to tweak settings for all jalview users.