ANN: Swift version of Grocery-Sync demo app

[Jens Alfke]

I finally found the time to dive into Swift, and ported Grocery Sync. It's checked into a branch called "swift".

I also took the opportunity to simplify the Grocery Sync source code (both languages) and update the README.

—Jens

PS: Thanks to Mirco Zeiss for his swift-couchbaselite-cheatsheet repo, which helped me get started!