swift-3 branch incompatible with Xcode 8

[SteveCaine]

Attempting to build and run the FlowDemoApp project in Xcode 8.3.3 fails with two issues:

1. 'Swift Language Version' in the app and test targets still reference Swift 4 instead of Swift 3 (do a global search for 'SWIFT_VERSION' to find these).

2. The file "ProfileHeader.xib" has been saved in Xcode 9 format with 'Use Safe Areas Layout Guides' enabled. Disabling that checkbox and changing the file's 'Opens in:' popup to Xcode 8.x fixes this.