Rewrite settings system to accommodate multiple providers
Add interface calendarClient.
Modify eventsCalendarClient to implement calendarClient. Add linticketCalendarClient
Properly initialize the variable as an array
Include linticketCalendarClient
Require that event pingers suppply a provider key.
Implement providers in dak_event_xmlrpc
Require a provider parameter when doing ajax-based import and purge.
Update user interface woth proper controls for purging and importing providers