macOS system extension

[jagerman]

Still needs:

• Wiring up lokinet start/stop from the GUI
• Script to package the GUI + sign everything

[jagerman]

Now works. Relies on oxen-io/lokinet-gui#17

[jagerman]

We have a new mac icon (added as an svg here and built during the build), but it still requires some tweaks (that can come in a separate PR though).

[jagerman]

The way this now works is the following. It is dumb, but this is macos and apparently that's how Apple wants it to be.

// If we are invoked with no arguments then exec the gui.  This is dumb, but there doesn't seem to
// be a nicer way to do this on Apple's half-baked platform because:
// - we have three "bundles" we need to manage: the GUI app, the system extension, and the Lokinet
//   app (this file) which loads the system extension.
// - if we embed the system extension directly inside the GUI then it fails to launch because the
//   electron GUI's requirements (needed for JIT) conflict with the ability to load a system
//   extensions.
// - if we embed Lokinet.app inside Lokinet-GUI.app and then the system extension inside Lokinet.app
//   then it works, but macos loses track of the system extension and doesn't remove it when you
//   remove the application.  (It breaks your system, leaving an impossible-to-remove system
//   extension, in just the same way it breaks if you don't use Finder to remove the Application.
//   Apple used to say (around 2 years ago as of writing) that they would fix this situation "soon",
//   but hasn't, and has stopped saying anything about it.)
// - if we try to use multiple executables (one to launch the system extension, one simple shell
//   script to execs the embedded GUI app) inside the Lokinet.app and make the GUI the default for
//   the application then Lokinet gets killed by gatekeeper because code signing only applies the
//   (required-for-system-extensions) provisioningprofile to the main binary in the app.
//
// So we are left needing *one* single binary that isn't the GUI but has to do double-duty for both
// exec'ing the binary and loading lokinet, depending on how it is called.
//
// But of course there is no way to specify command-line arguments to the default binary macOS runs,
// so we can't use a `--gui` flag or anything so abhorrent to macos purity, thus this nasty
// solution:
//   - no args -- exec the GUI
//   - `--start` -- load the system extension and start lokinet
//   - `--stop` -- stop lokinet
//
// macOS: land of half-baked implementations and nasty hacks to make anything work.

[majestrate]

other than the cmake ponderings this looks good to merge