Fix CONFIG_START/CONFIG_END

## XCTest fixes

Sets up `KWConfigurationTestObserver` in `+[KWExampleSuiteBuilder initialize]` to respond to `-[XCTestObserver startObserving]` and `-[XCTestObserver stopObserving]`.

Also moves `TestSuiteConfigurationAdditions` into the SenTestingKit subdirectory, and removes it from the XCTest static lib, to disable the method swizzling implementation under XCTest.

## SenTestingKit fixes

A patch is pending here (just needs some testing and tidying up). I don't think SenTestingKit support should be completely dropped in a minor release, so I'd still like to have this fixed for v2.3.0.