Change max length of external to 96 char in validation

[joe-irving]

• Changes max length of external ID from 12 to 96 in import validater
• Changes Swedish and English warning messages from 12 to 96

Resolves #1326 on front end, @richardolsson to double check that back end is okay for longer external IDs

[richardolsson]

@niklasva82 can you review this, and make sure it works with backend?