Bug 6875 de-nesting C4::Koha.pm

Bug 6875 de-nesting C4::Koha.pm

* removed use C4::Output, that was not used
* moved use URI::split to getitemtypeimagelocation and switched to "require".
  Checked it still works through admin/itemtype.pl
* moved use Business::ISBN to _isbn_cleanup.pl and switched to "require".
  Checked it still works with the following small script :

use C4::Koha;
print GetNormalizedISBN("1-56592-257-3");

(GetNormalizedISBN uses _isbn_cleanup)

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>