Adding option to save and load state by mtime

Load last state is expanded to 8 actions, for newest to oldest state

A new action is to overwrite the oldest state (or use an empty slot if available)

The code to wait for a save to be written is necessary because the alternative would be to keep track of files in queue to be saved which would be unnecessarily complex

Adding remaining hardcoded state keys to hotkey dialog

Adding a program exit hotkey