Add primitive Undo/Redo support for resource edits

[PhotoNomad0]

We can use the git commit history on DCS to navigate backward and forward the git commit changes to allow reversion of edit changes. Note that if there are unsaved changes on the card, we should save those before pulling in old commits. That way redo would work if they have second thoughts.

Notes:

• this would not be as granular as the undo in a text editor (but in most browsers they already have that capability by doing CMD-Z
• need to test - this may not be fast.