More structure refactor

I have finished refactoring the structure.
Now it has 2 main namespaces: `Compute` and `Parsers`, each of them within its own folder.

The `Fog::XenServer` will automatically define the constants `Fog::XenServer`, `Fog::Parsers` and `Fog::Compute` each of them on its own file and requiring its related files.

The code and names remain the same, i have changed only the folder and files to make it easier to find the models by just looking at their names.

This pull request became too big (If i had splitted it, i would have to create several pull requests which would be dependent of each other :expressionless:), but i did several commits splitting the changes, so it would be easier to review, i expect. :fearful: