Linked entries in the History queue

[mattlag]

For Global Actions that affect Components and Glyphs / Ligatures, we don't put that change in the History queue to enable Undo. This is complicated because Undo queues are per-page (Glyph Edit / Components / Ligatures) and some global actions have effects across pages.

Need a new concept of an entry in a single Undo Queue that is also linked to other pages' Undo Queues, and rolling back this special Undo would reach across pages to make changes appropriately.