CTRL+Z support

CTRL+Z to undo changes.

This could potentially be done by:

1. Creating a keypress listener for the document window, and listen for CTRL and Z
2. Creating a stack in Workspace or State that contains commited actions
3. Add a function to Workspace called "Commit" which commits an action and how said action can be undone.
4. Pressing CTRL+Z will navigate backwards through the stack

Start by locating the document-window input handling and the Workspace or State action flow mentioned in the issue. Trace how committed actions are represented before deciding how undo should navigate them. Done means CTRL+Z reverses the most recent change and continues undoing earlier changes in the correct order.

Written by the indexing model from the issue text.