Bring Mutlislice Ptycho to feature parity with FancyPtycho

Aknur is doing some work with the multislice ptycho model, and has noted a few issues with it. This includes issues on the documentation side. Let's use this issue to accumulate problems we note with the model, and we can open a tracking PR to implement changes and update the docs as appropriate. 

Those working with Multislice ptycho, please feel free to pile on here with complaints