Standard cleanup

[ajbeaven]

Just a quick spritz through the codebase:

• Removing used using directives
• Fixed typo in method name
• Removed commented out code
• Added additional references to the App Store Server API docs. There are a couple more models that don't reference a page in the docs, but I left them as I wasn't sure what they related to or (in the case of NotificationSubtype) the page I figured it was related to didn't line up exactly:
  • NotificationData
  • NotificationSubtype
  • DecodedNotificationPayload
• Removed or added whitespace where appropriate