Support GTIN-14 / EAN-UCC

currently only EANs with length of 8 or 13 are supported, but for some cases you also need different lengths like 14.
E.g. http://www.ibcaweb.org/guide/guide_mfr/ch4.htm#4.4%20EAN/UCC-14%20and%20Intermediate%20Packs