Fix EZP-22617: Add API integration test for ISBN and fix missing parts
Fix EZP-22617: Move validation, make strict and remove left overs

Fixes review remarks.

In restrospect this field type should have been based on TextLine or
similar FielType, most of the issues with getting this to work properly
can be attributed to the fact that it was copied from Country which has
a different data structure and different validation needs.
Merge pull request #852 from ezsystems/ezp22617

EZP-22617: Implemented ISBN Field Type