trade: review Valuation Method field on Inventory Report

 - add an empty item to the list, so that user have to choose something
 - translate values
8 jobs for fix/inventory-report-form-small-fix in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner2

00:46:20

passed ERP5.UnitTest-TestRunner2

01:42:53

failed ERP5.UnitTest-TestRunner2

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canceled ERP5.UnitTest-TestRunner2

failed ERP5.UnitTest-TestRunner2

02:58:34

canceled ERP5.UnitTest-TestRunner2

failed ERP5.UnitTest-TestRunner2

01:33:39

canceled ERP5.UnitTest-TestRunner2