I can sort Spreadsheet View on a column

(User Story, To be Fixed , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Spreadsheet View
Summary: Ideally, this is a little v/^ selector that appears when you hover in the column header, but make sure it works for small screens.
This sets a Sort Model By Property on the Model, which uses _sort() normally internally. _sort() should get enhanced so that, if you pass in a List or Set of Instances, and this Property is set, it sorts by that by default.
Ideally, you should be able to sub-sort on additional columns, but think about the UX pathway for that. Does, eg, Excel establish a de facto UX standard for this?