Add string translation to auto approval option

Created by: phellmes

The description for the auto-approval option was not translatable. The t-function was also missing on the Yes-option of the switch. I put the switch array into a $yes_no variable with translatable strings as it is done on other settings pages. There's just one switch on that page now but it's more consistent should there be added more later.

Note: Looks like my editor catches a lot of space characters at the end of lines and removes them when saving the file. Should I switch that function off or is it okay if the files are cleaned that way? I like files without these unnecessary characters but the removal can make commit diffs a bit hard to read here.