Adds option to use a quicksave rotation

[khutchins]

This adds the ability to use a rotation of quicksaves instead of manually specifying a quicksave slot at the time of first saving. It also adds the ability to specify the size of the rotation, as the autosave rotation allows. It is disabled by default to avoid changing behavior for existing users.

A quicksave rotation avoids the hassle of having to specify a save slot on launch, and it also helps avoid situations where the player unintentionally quicksaves right before death, by giving them an opportunity to load an earlier quicksave instead of the autosave at the beginning of the level.

Strings:
MISCMNU_QUICKSAVEROTATION = "Enable quicksave rotation"
MISCMNU_QUICKSAVECOUNT = "Number of quicksaves in rotation"