cubicweb-book #4553153 set unique=True for isbn10 and isbn13 [validation pending]

books with the same isbn are the same, no need to describe them twice. add a ticket to include BookItem -exemplary-> Book if needed (FRBR-style)

prioritynormal
typebug
done in0.7.1
load0.100
load left0.000
closed by#96a981d7bbd1 [schema] set unique=True for isbn10 and isbn13 (closes #4553153)
patch[schema] set unique=True for isbn10 and isbn13 (closes #4553153) [applied]