Add option to keep aesthetic model in ram

[SOELexicon]

as title would suggest. having the option set to one. drops generation time for subsequent runs from 13 seconds to 3.69

Prompt executed in 13.44 seconds // first run to load the model in memory got prompt DDIM Sampler: 100%|██████████████████████████████████████████████████████████████████| 20/20 [00:00<00:00, 30.27it/s] Prompt executed in 3.76 seconds // subsequent run that uses the model loaded from memory