Add DICOM tag browser

[fedorov]

Ability to view DICOM tags is important to see attributes not exposed in the UI, and would make Slim similar to radiology viewers in the capabilities.

Need to investigate the size of the tags for representative samples from IDC and discuss the design of this feature before the implementation.

[fedorov]

Feedback based on review today:

• need to be able to select every series in the study - not just the slides
• instance 3 is missing the label in the scroll bar (or maybe it is missing in the files?)

• when searching, it would be helpful to have an option to show child items for a parent that matches the search string even if the child does not

[igoroctaviano]

@fedorov PR is still open. @pedrokohler can you review? #251

[fedorov]

Really nice work!

Can you add make it such that if child is matched by the search, all of the parents are displayed as well?