Deal with large number of tabs better

[blernermhc]

If you create a lot of DDGs (e.g. by examining many breakpoints), the tabs do not fit in the window. The default behavior on Windows is to run over to a second line, etc, because the tab titles are so long (script name plus date-time plus time zone). On Mac, the tabs become scrollable. It would be preferable for them to be scrollable on Windows as well, which involves setting the tab layout policy of the JTabbedPane.

We might also want to consider using shorter names in the tabs and putting the full name and timestamp inside the tab contents instead of in the tab's name.