Return of the Object-Oriented API

[brandondube]

The changes from prysm v0.19 to v0.20 basically deleted most of the object oriented-ness of the library. This has made it easier to write prysm, but the API is pretty radically different to its contemporaries (PROPER/POPPY/HCIpy/FALCO). This can be intimidating for some users, who may not be familiar with or want to learn this.

We should consider building out an object oriented API more similar to other projects. The core propagation and interferometry modules are already really object-oriented. Maybe this is a concept of OpticalSystem (from POPPY) that is missing.