Sort parts by the order attribute

Sort the list of parts by the value in the order attribute, so that
changes to the order are persisted when the edit form is reloaded.
Ensure the array of parts is in the correct order

Order the array of parts by the 'order' attribute before saving
a travel advice edition.
Revert "Sort parts by the order attribute"

This reverts commit 467c98b7e37b5214e8f2e51a375e1fd7b0d55023.
Merge remote branch 'origin/sort-parts-by-order'