Provides a single-point access for modifying the schematic and symbol
elements that allows chaining updates and reverting partial changes.
Standardizes the undo hierarchy between pcb and schematic editors
As this is another layer on the existing undo/redo structure, the
initial commit does not replace all undo/redo calls currently existing.
These will be handled in a series of follow-on commits
Marek Roszko
Seth Hillbrand