Publishing to macOS app store

This is for tracking the various findings/changes needed for publishing the bitmask-vpn to app store

• Use NetworkExtensions for the VPN connection
  • implement a go (cgo <-> swift) wrapper library using TunnleKit
  • modify bitmask-vpn to use network extensions (provided by the library) for the VPN connection
• move post-install and pre-install setup out of the qt installer and into the app
• submit app for review