With latest simulation, the explanation given to user when solving a
divergence was not good enough :
- Property ids were displayed without possibility to display
  business word (like displaying 'stop_date' instead of
  'Delivery Date'
- Some message was displayed in the solve divergence dialog whatever
  was the equivalence tester behind. Therefore, customizations of
  messages made a equivalence tester level were not displayed to user

Therefore, following was done:
- in solve divergence dialog, include the message generated by the
  equivalence tester
- use tested_property_title to allow using business words to describe
  properties having divergence
- most equivalence testers are written in a way to evaluate divergence
  on a single property. To have better UI configuration of such equivalence
  testers, change tested_property and tested_property_title properties
  type from "lines" to "string". This required to add some backward
  compatible code.
- use Variation Divergence Tester to show a case of an equivalence
  tester using different properties. For this, add a property sheet
  dedicated to multi properties equivalence testers
- update propertysheets to allow translating tested_property_title