AFWA-57 WIP: Added invite actions on App server. Invite works. Need to implement other client invite actions to test.
Major changes:
 - Improved error messages for /call API.
 - Added enum package.
 - Added Enum:
  -- RegStatus
   --- User's registration status, including state of database record
  -- ActionType
   --- Type of API action to be performed.
  -- CloudType
   --- Type of cloud notification, e.g. ADM, GCM.
 - sendEmail to include ActionType
 - Create sendCloud by merging sendADM and sendGCM
  -- takes CloudType to use appropriate cloud.
  -- takes ActionType to send appropriate message.