Support Swift tests

[wearhere]

This bug tracks necessary changes to support tests written in Swift. It does not cover migrating Subliminal itself to Swift.

To-do:

• Code changes
  • re-implement the UIAElement macro as a function
  • re-implement the SLTest assertions as functions
• Documentation changes
  • Provide Swift file templates (probably as language options for the current templates, like how Xcode 6's "new class" templates work)
  • Provide an example of a test case in Swift on the wiki
  • Note that it might be preferable to continue to write test cases in Objective-C until rdar://17239947 is resolved

[wearhere]

This is blocked until Apple fixes UIAutomation in Xcode 6: rdar://16813256.

[wearhere]

This is unblocked. Work should be done atop shared/xcode6 (see #259).