[Feature request]: Rotating quicksaves/autosaves, more functional save system

[SinaelDOverom]

The basic idea: separate slots for quicksaves and level-start-autosaves. Every time you quicksave, don't overwrite the quicksave and save in a next slot instead, when last slot is reached, start from the beginning overwriting the first-by-date.

Same way similar option works in GZDoom. Maybe add option to take/display save screenshots if available.