[Feature Request] Allow selection of one specific custom palette and allow browsing with L& R

[schmurtzm]

It could be interesting to allow the user to have his own set of palettes instead of the colossal collection directly included in the core.
The option to browse palettes with L&R is very great but the feature is useless with the actual number of palettes.

It could be nice for the use to be able to select one of his custom palette directly from core options and then be able to switch between his own custom palettes with L & R.

A preview of the palette could be nice too but it would require some retroarch modifications I suppose so that's another subject.

By the way I would arg that more than 40% of the weight of the Gambatte core is due to TWB64 palettes names which are translated in 39 languages.