combine .atacCompartments and arrayCompartments workers into getCompartments

[jamespeapen]

getATACABSignal and getArrayABsignal had much of the same logic. Now with the assay argument, they can be called from scCompartments or getArrayComparments arrayCompartments. getATACABSignal is no longer necessary as scCompartments can call getCompartments directly.

For functionality and consistency the boot.parallel and boot.cores args have been added to scCompartments and reorganized into groups relating to parallelization and/or bootstrapping.

getArrayCompartments is now arrayCompartments to be consistent with scCompartments.