Fix issues with building/packaging RealmBrowser.app with build.sh

Instead of using `Realm.xcodeproj` as a subproject to `RealmBrowser.xcodeproj`, use the same approach as examples ("Realm" aggregate build phase that runs `sh build.sh osx` only if the framework isn't built).

Also copy `Realm.framework` into the resulting app bundle so the browser app is self-contained.

@tgoyne @alazier @GreatApe