Standard dunder/magic methods for Ontology

[CasperWA]

It might be nice to implement some standard dunder/magic methods for the Ontology class facilitating standard logical operations on Ontology objects. This is at least true for equality (==).

This issue comes from the fact that we (@francescalb and I) wanted to test whether two instantiations of the Ontology class from the same file were equal or not. (Here is a reference to the failed test.)

It might be good to implement other dunder/magic methods as well, maybe even for other classes as well?
For more information on the special methods, see the Python documentation or perhaps this guide written in 2012.