add undo and redo in Edit Menu; move to using 2 dim vectors instead o…

[MarkE16]

…f objects

Description

Include a brief summary of the changes added.

Fixes #(issue) (If not fixing an issue, explain what this pull request is for.)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that causes changes to existing functionality, possibly impacting existing features)

Have you tested your changes?

• I wrote tests for the code I've written.