Make locus-specific points visible in all z slices

[vreuter]

So that users don't need to scroll as much to get the critical information (did a particular (FOV, timepoint) pair have a locus-specific spot that passed or failed QC) we could make the point visible in all z slices. To preserve the information about where the center of the point was detected, we'll have shape determined by z and color still correspond to QC pass/fail status (instead of having them be redundant as is currently the case). Specifically, blue will be QC fail and red QC pass, with * reserved for the point shape in the z slice closest to where the centroid was detected, and o elsewhere.

[vreuter]

Confirmed w/ @TLSteinacker

[vreuter]

Closed by #13