Comments on model interface NB

[ammarcsj]

Hi Feng, I changed a few things around, based on the already comprehensive documentation you had in the notebook. In particular

• I renamed the class to ModelInterface, I thought this could be informative enough as a name, because we know from the context of the package It will have to do with peptides. Also because it is a 'Interface' we can expect it to be at the 'base'. Let me know what you think.
• use_GPU changed to set_device as we talked about
• some more docstrings and markdown comments where I thought they could help
• some function renamings and slight refactorings

[jalew188]

@ammarcsj Thanks a lot for the useful comments and updates, I have updated a few codes.