Download experience improvements

[fedorov]

• there are two download folder selectors

* remove the second download folder selector

• add back the separate download button that has the option to import or not into DICOM database; when import into DICOM db is selected, behavior would be identical to downloading using bottom right button (except for the manifest, which can only be downloaded using left panel)

• cancel button does not cancel

  • need to terminate download

• progress bar seems to increment in 1s of units it shows (MB/GB/TB) - too coarse when downloading large subsets

  • pick increments based on the total size? ( BUG: Fix download progress bar increments #68)

• selection of the download destination in the left panel does not seem to have effect on where the files imported into DICOM db are - they should only be downloaded to the selected directory and not copied anywhere else

• use text widget that has cancel button in the right side to clear the field - something like this

• when there is not enough space, we know this in advance and don't need to initiate download - report insufficient size in the left/right panels for the selection? Depends on Raise exception when there is not enough disk space idc-index#194

[fedorov]

Depends on ImagingDataCommons/idc-index#194

I added that feature and tagged new release of idc-index 0.11.1 to include it. Let me know if something is not working as expected @Sunderlandkyl.