New methods for SyncOntology and SyncReasoner

[alkidbaci]

Added new methods for SyncReasoner:

• is_entailed → checks if an axiom is entailed by the set of reasoner axioms.
• is_satisfiable → cheks if a class expression is satisfiable with respect to the reasoner axioms.
• unsatisfiable_classes → retrieve classes that are unsatisfiable

Added new methods for SyncOntology:

• get_signature → retrieve all signature entities.
• get_abox_axioms → retrieve all ABox axioms.
• get_tbox_axioms → retrieve all TBox axioms.

[Demirrr]

Thank you for the PR. Can you please write tests for the each introduced methods ?

[Demirrr]

very cool features!