Fix labelling errors in the Download DICOM tool

[Zach Pearson]

From an email sent by Elaine:

(5b) The "Back to Databases" button should be "Back to Database" since you are only looking at one database at a time. Actually should be "Back to Collections" if we're thinking only of TCIA, but maybe other databases will have other terminology for top-level groupings of studies.

(7) Something seems to be wrong with the "Number of Series" column in the list of collections (the top level of the TCIA database). E.g. collection "QIN Breast DCE-MRI" is reported as having 10 series. However, if I highlight it and drill down to studies, it contains 20 studies and each of those studies has 34 or 30 series in it... so 10 is way off. Maybe that column is unnecessary anyway; would be more useful to have the same columns as when browsing TCIA collections on their website (possibly minus "Access").

(8) Name of the tool itself. Many other DICOM viewer programs use "DICOM Database" to mean the user's own local cache of previously obtained or downloaded data, rather than an online repository. So I was thinking maybe something along these lines would be a better name:

DICOM Fetch
Fetch DICOM
DICOM Browse/Fetch
Browse and Fetch DICOM
Download DICOM

[Zach Pearson]

​This ​pair of commits renames the tool (8), corrects the column to say "Number of Patients" (7), and changes "Back to Databases" to "Back to Collections" (5b).