Standardize top level compartmap finding functions

[jamespeapen]

The current top level functions are scCompartments and getArrayABSignal. The docs for plotAB reference a non-existent getCompartments function. These should be unified or the names standardized.

[biobenkj]

Agreed on this. The plotAB function is a legacy thing too for a "quick look" and can include the variance estimates as well (which is quite handy). I'm open to extending this to produce prettier plots as well.