country.cgi: Cosmetic fix for 'Back'-button'

country.cgi: Cosmetic fix for 'Back'-button'

While testing Peter's patch for Bug #12560 I noticed that the standard 'back'-button
at the end of the page - like in 'ipinfo.cgi' - was implemented as a text string.

I just took the code segment with the 'back'-*image* from 'ipinfo.cgi' to make this
link looking similar to the other pages.

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>