Moving 'Count The Days Left' to Swift 3

Version 2.3 of Count The Days Left has now hit the App Store for your viewing pleasure.

I finally got around to upgrading the code to Swift 3. The Xcode migration code did a reasonable job with the syntax changes, but missed a few things around interface changes - especially in the WatchOS code - that I had to fix manually.

I also fixed a very minor logic error in the date calculation in the settings page. Quite amazing it had been sitting there in plain sight for a long time without me noticing it.

Not much more to do in the app right now, but maybe WWDC in the summer will bring some exciting new areas in which to play in?