Add a "compose payload" view

[jchambers]

Constructing APNs payloads is a non-trivial task. Rather than requiring users to manually enter complicated blobs of JSON, we should add some kind of "compose payload" tool.

[jchambers]

I think it makes sense to focus a "compose payload" view on the latest generation of payloads. Via "Generating a Remote Notification," the things we'd want to cover there are:

• alert
  • title
  • title-loc-key
  • title-loc-args
  • subtitle
  • subtitle-loc-key
  • subtitle-loc-args
  • body
  • loc-key
  • loc-args
  • launch-image
• badge
• sound
  • critical
  • name
  • volume
• thread-id
• category
• content-available
  • Setting this to true should disable the alert, badge, and sound inputs
• mutable-content