Add option for folders to not be counted as tabs in the tab counters on folders

[robbyph]

I'll be honest, I have a lot of tabs open usually, which is a big draw of using this plugin.

By default, sidebery counts folders as "tabs" for the little tab count indicator that comes up. When I have a bunch of nested folders, this throws off my page count.

Would it be possible to add this option, so that the little page counter widget only counts the actual tabs open, and not any subfolders that may be present? But of course keep counting the tabs within those folders.