RG cell's width resize to fit RG width (based on cell count)

Have a single row RG that functions as a Tab selector, i want the tabs (Cell) width to expand and shrink based on the Tab (Cell) count, like the behavior of the tabs on a browse: when you remove or add a tab, the tabs resize to fill the total space.

Also i want to have that “+” tab at the end so users can add a tab (Which is actually another entry in the database)