Figure out how to handle copy support

[Kingdutch]

The socialbase theme currently has a gulp task specifically for mime-icons that's implemented as follows:

// #################
//
// Image mime icons
//
// #################
//
// Copy the mime icons from the components folder to the assets folder (manual task)
// ===================================================

gulp.task('mime-image-icons', function () {
  return gulp.src(options.icons.src + 'mime-icons/*.png')
    .pipe(gulp.dest(options.basetheme.build + 'images/mime-icons/'))
});

This task seems to have been unneeded for a long time but being able to configure copying of certain folders is a useful feature.