Module and Submodule organization.

[duartepinto]

Currently, we are exposing all classes. It would be nice to research about Submodules and Modules in Objective-C to see if we can set some of the classes (like VSDKUtil) as Internal classes and only expose the classes that we want. Even if we end up exposing everything, it would still be cool to have a proper Module and Submodule organization for better Swift interoperability.