The _getOrderedList approach was not ideal, because the properties were
saved when being displayed, so the typical workflow was:

 1. enter the property as non sorted
 2. click save (property is saved as non sorted)
 3. the page displays the property again as sorted
 4. click save again so that the property is saved as sorted

by sorting the properties at save time, step 1 is enough

This change back the accessors to be "standard" accessors, ie. returning
lists, like every other list accessors, so a few tests and a few scripts
had to be adjusted for the new API.