Save ReplayGain values not in the music files, but in the internal database

[SonicRings]

I'd like to calculate ReplayGain tags for my entire library, but I do not want the date modifieds of my folders to update, nor do I want to actually change the tags of my music files.

I figured it would be no problem to simply have an option to let us save them in the internal database as either a custom tag or virtual tag.