Embed the examples logic into the pipeline

[mspronesti]

Hi @LaurentMazare,
now that this repository has expanded more and more, I was thinking we could move most of the code of the examples inside a StableDiffusion pipeline, as HF does.

This would also allow us to support more features, such as negative prompts and then support more diffusion pipelines, such as latent diffusion and so on.
Do you think this is a good idea ? 😄

[LaurentMazare]

Hey, sorry for the delayed answer, yes that would sound like a reasonable idea: there is already a pipeline directory with a stable diffusion module in it and moving a bit of the code in there from the example would make a lot of sense.