ESRGAN

[victorca25]

Following from #1322 and the Contributions guidelines, I can try to work on a single ESRGAN network that works for real-ESRGAN and ESRGAN (including all the ESRGAN models in https://upscale.wiki/wiki/Model_Database).

@AUTOMATIC1111 I don't know how many line changes it will end up being, but it should be mostly limited to the ESRGAN networks files, and no application logic should be affected. I'm just checking with you before working on the PR.

[victorca25]

@d8ahazard @AUTOMATIC1111 I have the code already working locally, all the ESRGAN models in the database should work now, as well as the BSRGAN model (which also used the same architecture as ESRGAN). I'll try to submit the PR tomorrow, but I have some comments:

• The 1x models work, but currently the app skips running the models if scale = 1
• There are models with scales larger than 4 (8x and there are even 16x not in the DB), but the app has a max of scale 4
• The BSRGAN model and arch files are not needed and I will suggest removing them in the PR
• I can also work on making the real-ESRGAN models work with the same architecture, but a bit of a dependency exists in the application with the models that can be downloaded automatically with the get_realesrgan_models() function.

The first 2 points are not a major issue, but will need some thinking about how to go about it, also because the same slider is user for every upscaler option.

About the last point, it would be irrelevant if a separate list of the default models are kept in a central place and can be sent to the "model downloader" function (maybe one that does not depend on basicsr), which could include not only these real-ESRGAN models, but maybe also BSRGAN and any other.

I will mention these points in the PR as well, just wanted to bring them up beforehand just in case there are any comments.

[kroaton]

Awesome job, mate!