add Apple Shortcut support for processing passed images

Proofmode iOS should support being called as an action within Apple Shortcuts.

You can create a shortcut that is automatically triggered every time the camera app is closed for instance.

You can also trigger a shortcut that starts the camera, and then passes the resulting media to another shortcut.

We can then easily share/promote the shortcut from within the app, or from our website. Easy one click install.

This is a hack way to get "integration with the native camera" aka "auto sync" mode working.