add fb algorithm, pnp-prior functionality, abstract classes, and kera…#12

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CosmoMatt wants to merge 2 commits intomasterfrom

Feat/Learned_FB

Commits on Mar 9, 2022

add fb algorithm, pnp-prior functionality, abstract classes, and keras gradients
CosmoMatt
committed

Commits on Mar 17, 2022

explicitly pull out theta acceleration in primal dual
CosmoMatt
committed