Bulk modification of canvases (labelling etc)

[tomcrane]

(split from #134 - read the common points in that issue too)

This issue isolates the automated data-modification of multiple canvases (e.g., auto-page-numbering) from the selection, reordering and moving of canvases.

The same issues of SELECTION apply, but they would be met by the selection mechanisms discussed in #134, then could be applied for applying actions to those selections.

(from #134)

This is an App that is used for foliation, pagination, bulk labelling etc.

It has already been mentioned in #41, but here's a distinct issue for it.

Another Canadiana use case is

Ability to put items in either chronological order or alphabetical order (Heritage reels)

This would fit in this app. Also a nice UI for assigning navDate and maybe navPlace to canvases.