Fix compilation with the Xcode 6 GM

Disables Swift support on OS X for now as 6 doesn't support it and we currently
don't support 6.1
Merge pull request #896 from realm/tg-xcode6-gm

Fix compilation with the Xcode 6 GM
updated examples structure to use a single Xcode project per platform/language combination
fixed osx/objc/RealmExamples
- shared all RealmExamples schemes
- added package_examples.rb
re-added realm files for Migration examples
attempt to fix conditional ios framework build phase in ios/objc/RealmExamples
attempt to fix CI by cleaning for every target in RealmExamples
another attempt at fixing CI
Fix the framework search path for the examples
Set the executables to run for the example projects
Merge pull request #879 from realm/jp-examples

New examples structure and packaging
Rewrite the Swift class support in Objective-C

Turns out that you can't use Swift in a framework on iOS 7, so move everything
but the convenience functions in Objective-C and switch to building a static
framework. The remaining Swift code is left in a single file which must be
included directly in the user's application (if they want to use it).

This happens to add support for optional RLMObject properties in Swift.
Make the path to Xcode overrideable with the XCODE_PATH env variable
Clean up some stuff
decouple code paths for parsing properties for objc vs swift
Fix running iOS tests from Xcode 6
Update changelog
Merge pull request #901 from realm/tg-swift-ios-7

Rewrite the Swift support to work with iOS 7
Improve attributesForProperty: documentation

Actually explain how to use it and add an example.