Add "same chart in new tab" option when selecting multiple files (or tags)

[giltene]

Currently, when selecting multiple files, the options available are "same chart" (which opens a new chart in the current tab), "same tab" (which opens multiple charts in a new tab), and "multiple tabs" (opens a single new chart in each of multiple tabs).

The full set of options should be "same chart in new tab", "same (new) chart in current tab", "new chart in current tab", and "new charts in multiple tabs".

The first is commonly needed for side-by side comparisons of multiple files (e.g. 4 hicuups vs. 4 control hiccups).