Adding clip encoder for generation

[neonsecret]

Okay so I know I changed a lot and it might be too much for 1 pr, but almost all the changes are purely folder reformats to support different DiT subarchitectures better.

The new one I added is a DiT with frozen clip head, which, instead of taking imagenet classes as an input, takes a text prompt.
See sample_gradio.py and modules/dit_clipped.py for more info.

I am yet to train it to see if it will yield results, but if you guys think it's a rational venture, we can agree on how to merge our PRs and work on this old-new architecture together.

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