Combining the PS-selection with SHP-finding and phase-linking

[scottstanie]

Currently PS selection happens in a separate step. This means we load the data stack once, save/update the PS, then reload all blocks to phase link.

Should we do the PS selection + SHP finding + phase link all in same loading period?

The timings in #6 show that when we calculate PS on a whole stack, the loading time is the majority of the time and we'd get a large improvement by only loading stack blocks once.

But, it won't be as a big a speedup for online-updating of the PS, where we'd only pull and iterate over 1-2 SLCs to get a new PS map. Thus this is low priority.