Implement undo function

[andy5995]

This function is dependent on #5 and #9

On a single run, when files are rmw'ed successfully, the absolute path names of their destination in the Waste/files folder are written to a single undo/mrl(most recent list).

When an undo is requested, the file is read, and each filename is restored using the restore function (#5). If no errors occur, the mrl file is deleted.