RestGrid should have visible last refreshed timestamps

[lbwexler]

Could be optional, but would be highly useful in the main grid toolbar, and also the dialog popup.

Good reminder that what you are looking at is not necessarily the latest and greatest.

Tom and I discovered while testing consistency with multi-instance, but really not related to that.

[amcclain]

I'm for it, although agree we should make it optional. I'd like to take the opportunity to review how we spec / arrange the toolbar items in general - would be nice to allow the developer more control, eg by providing a list of string tokens ala grid contextMenu. For instance, I have started to more eagerly place a column chooser in grid toolbars - would like to enable for some rest grids.