Add autocompletion for namespaces (IPython only)

[kysrpex]

This pull request aims to solve issue #591, at least for IPython users. The idea is to modify the __dir__ method of namespaces to include their ontology entities, so that auto completion is offered. A similar thing could maybe be done for the namespaces.py files, I still have to do more research on this.

To Do list to complete the pull request

• Add autocompletion for Ontology Entities inside a namespace.
• Add autocompletion of namespaces (when writing osp.core.namespaces.[...]).
• Write unit tests for both cases.

[kysrpex]

Updated the checklist (added autocompletion for namespaces).

[kysrpex]

Updated the checklist (added autocompletion for namespaces). This will only work if the user first imports the namespaces module, i.e. import osp.core.namespaces as namespaces. Then autocompletion will be available for the namespaces object. I think it is not possible to autocomplete the statement from osp.core.namespaces import <...>.