gsr-fileutil: create separate function for folder

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
add open_folder_cb function

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
do not handle files as command option

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
remove useless filename dependecies

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
use cached version of basename

Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>