Move "Show in Groups" toggle action into Sort menu

Move "Show in Groups" toggle action into Sort menu

This is the sort of thing a user might want to toggle temporarily, as
sometimes grouping is a helpful visualization and sometimes not.

Right now, doing that is easy when using the in-window menubar or the
global menu: View > Show in Groups. However when using the default
hamburger menu, it becomes difficult: Burger menu > More > View >
Show in Groups. It's four levels of nesting and requires precision.

This change addresses that by  moving the action into the "Sort By"
menu. This improves discoverability for people using the default UI,
and makes the location of the action consistent for people using all UI
styles. It also gets the item into the view context menu, where it
currently isn't, providing another entry point for it.