Data Browser UI Upgrades

[PaulHax]

• Unify backing store for DICOM and Images UI. feat(KeyboardShortcut): Add left and right arrow to cycle through images #611 (comment)
• Unify DICOM and Images Vue components. Put images under an anoymnous patient section and reuse component code for DICOMs and images.
• Fix visbility status of layers and segment groups usablity issue. Folks are confused when a CT and PET are loaded together and the PET gets layered as a heatmap automatically. Also consiter our automatic conversion of images to segment groups.
• Communicate to the user when segmentation series is being loaded #687 (also for Layers)