Update to Swift 3

[brody4hire]

A temporary solution is described in http://stackoverflow.com/questions/37835397/use-swift-2-2-in-xcode-8/39519881#39519881. But this will go away.

In terms of dependencies:

• XWebView already uses Swift 3 in versions 0.11.0 and 0.12.0.
• For ActionKit there are two different Swift 3 contributions, I hope to see one of these integrated soon:
  • https://github.com/ActionKit/ActionKit/pull/26
  • https://github.com/innovactorybv/ActionKit/tree/swift3 as described in https://github.com/ActionKit/ActionKit/pull/20#issuecomment-251764404