Change tabs DIV grouping from multi-set to single-set

[bradleyrichter]

The Tab Sets organization provides quick access to subgroups of tabs, provides the ability to find noisy tabs quickly, and will eventually allow fast tab set previewing, re-ordering and bookmarking.

Unfortunately there is no way to scroll 1 of 2 or a few tabs at a time, and animation transitions are difficult to set up with the current organization.

current:

[tab][tab]….[tab8]

new:

[tab][tab]….[tabN]

The result will feel like a mix of FIrefox tab scrolling and Brave tab sets.

The current UI elements will be used and serve the same functions.