Refactoring suggestions

[alkidbaci]

Counter-intuitive issues with the current structure:

1. All owl objects are located in owlapy/model/init.py.
2. Conversion methods are scattered in 3 files render.py, parser.py and owl2sparql/converter.py.

Proposed solution:

1. Group owl objects by semantic meaning in different modules. Import all in owlapy/__init__.py
2. Relocate converter.py in the owlapy directory, import conversion methods in owlapy/__init__.py.

[Demirrr]

The first phase of the refactoring is done with #21. Please continue on the second phase defined by the following todos

• Instead of using from owlapy.model import ... we use explicit imports, e.g. from owlapy.owl_class_expression import ..
• Move the reamining class definitions (e.g. OWLOntologyID, .., OWLReasoner into a suitably named python script under owlapy
• Continue refactoring until owlapy/model can be removed.

In the third phase, we will create modules under owlapy to group individual scripts