add quick save option via screensaver shortcut

[w-winter]

Adds a new default behavior that is enabled by uncommenting https://github.com/warrenwinter/O_C/blob/5ff81313f65ddda4f3e749f53976a76de1d004b9/software/o_c_REV/OC_options.h#L34 : the module will then save all settings (identical to how it is done from the app selection menu) every time the user manually switches to the screensaver (using a given app's screensaver shortcut, e.g., long-press of the up-button in Quantermain).

I considered other single-action shortcuts for this but couldn't think of another that didn't present a functional conflict when changing app settings. Since this involves erring on the side of over-saving, it's offered as an option, which might appeal to some owners who want a single-action method for saving (e.g., those who also own a few other modules that require manual saves). Another cost is that manually switching to the screensaver now produces the pause that saving entails, but it's not the worst thing given that manually switching to the screensaver isn't critically important during performance.

[w-winter]

Apologies for the mistitled commit https://github.com/mxmxmx/O_C/pull/95/commits/70478e9601169a421d6c1ad8b7a383d66d8a257a .