Implement direct message receive and background services manager, take 1.

Implement direct message receive and background services manager, take 1.

 1. Background Service Manager Framework
    --Documentation provided in the main library/ajax/execute_background_services.php script.
    --Report at Administration->Reports->Services->Background Services
 2. Direct Message Receive
    --Service built on top of the Background Service Manager Framework
    --Can be set/modified in Administration->Globals->Connectors (bottom section)
    --Log can be viewed at Administration->Reports->Services->Direct Message Log
    --Added support for importing of documents with no patient mapping. GUI for
      this is at Miscellaneous->New Documents.
    --Added support for sending pnotes with no patient mapping.
    --Added support for service bots to enable storage of documents,
      sending of messages and accurate logging by services.

 Miscellaneous mods: Changed the Administration->Services to Administration->Codes in left_nav menu.
                     (to avoid confusion with the Services reports)