Added and changed existing data loading and saving

• Fixed existing names for json
• Added missing main elements for platforms, devices
• Tested with actual backend

The following stuff is still missing, but I would like to have those changes here in the master before we go on the remaining tasks:

• Load events
• Load properties
• Load custom keywords
• Load attachments
• Load contacts
• Save contacts
• Save properties
• Save custom keywords
• Save attachments