Fixed errors when importing journals CSV file

Since some ISSN's were malformed or not constructed in the expected format (e.g.: "1234-1234, 5678-5678", 1234-1234), an extra sanitising was needed to generate an ElasticSearch index. Because of the sanitising, malformed ISSN's will now be returned without commas and spaces. (e.g: 1234-1234-5678-5678-1234-1234).
Follow-up on review
Merge pull request #11 from Coenego/avocet-journals-fix

Fixed errors when importing journals CSV file