Replace the 100%-native wollok lists by a "partially native" wollok List class in SDK

[javierfernandes]

We need to provide a wollok List class as part of the SDK. Of course this class will be coded in wollok language. Although we will have some native methods. Eventually the list literals will end up instantiating this classes.

This has 3 main purposes

• Provide a class with wollokdocs and accesible code so that users can check the code and understand how methods are implemented, but more important read the wollokdocs and understand the intention of each message. Also the IDE will help providing content assist for List as well as static checks :)
• Simplify the interpreter code by having a consistent model where every object are either wollok objects (literals or named) or instance of wollok classes, but not "special" objects.
• Probably also simplify the type system since all the information of objects should be as part of wollok code, and there won't be any special rules.

[javierfernandes]

Done in feature branch

[javierfernandes]