1. Add "All" default option to top of the menu. It should be unchecked when no items are selected. It should be checked when all items are selected. When all items are selected, click on "all" should unselect all items. When some items are selected, "all" click should select all items.
2. Selected checkbox icon should be of brand blue color. Unselected icons are grey. Checkmark icon might look slightly different from new design, we will sync checkbox implementations/design in a separate task anyway.
During testing, please make sure that all places that use bs-select directive don't have regressions.