New examples structure and packaging

This PR was previously #645.

The current examples structure isn't working very well. We have to run `sh build.sh build` to build the framework in order to build the examples. This PR moves the structure around and only introduces a single Xcode project per platform/language group, with the appropriate Realm Xcode subproject. So the new examples structure looks like this:

```
examples/
    README.md
    ios/
        objc/
            RealmExamples.xcodeproj
            Encryption/
            Migration/
            REST/
            Simple/
            TableView/
        swift/
            RealmExamples.xcodeproj
            Encryption/
            Migration/
            Simple/
            TableView/
        rubymotion/
            Simple/
    osx/
        objc/
        	RealmExamples.xcodeproj
	        JSONImport/
```

The process to package examples for release is:

1. Install xcodeproj gem
2. Run `./scripts/package_examples.rb`
3. Move the `examples/` folder to the root of the folder to be zipped for release

@emanuelez let me know if you have any questions since you'll be the one integrating this in Jenkins.

@alazier @tgoyne could you please review?