Download DICOM tool: need to segregate by collection when drilling down to study, and by study when drilling down to series

[Elaine Meng]

Need to segregate studies by collection (if drilling down from >1 collection to studies) and segregate series by study (if drilling down from >1 study to series). They still get mixed up in the current daily build. Examples tested in 1.6.dev202302180254 (2023-02-18) just now, same result as images from 2/14 build sent earlier and attached to this ticket:

(A) highlighted UPENN-GBM and TCGA-UCEC collections, drilling down to studies has TCGA ones sandwiched between two sets of UPENN ones (image attached, shows start of TCGA ones, there are more UPENN ones below them)
(B) for studies -> series, one of the two highlighted studies has series numbers 1-3 and the other has series numbers 201, 1002-1007. These are interspersed in the dialog showing the series of both studies that were chosen. (both attached images)

[Zach Pearson]

​Studies are now sorted by collection, and series are sorted by study.