The `custom field long choice` aim to provide a way to deal with choices
with a big possibilities.
The `custom field long choice` allow :
- to persist different options in the database ;
- each option has a key, a text (translatable string), and eventually a
parent, and an internal_key
- every key can be activate or not. If the parent is inactivated, all
childs are inactivated
- the internal key have two purposes :
- link to an external csv file, with their own key ;
- add a special class to results, to allow custom layout.
Currently, the field exists, but some elements are missing :
- a script for CSV import
- possibility to select multiple items
- edition of options
- handle of option without parents
- tests are missing
