SignalServiceKit is currently a separate pod. This makes merges tedious
and error-prone. Ultimately, it slows us down. It might've made sense as
a standalone library before, but it's so tightly integrated now that it
isn't useful to have it be separate.
This changes that, and makes SignalServiceKit a "normal" target.
IMO, most of this change isn't that exciting—just a bunch of changes to
scaffolding. There's one slightly spicier change: our generated
`Acknowledgements.plist` is now a little more clever.
Co-authored-by: Max Radermacher <max@signal.org>
