Change the mainlang behavior to not return a nil if no lang found

[syphax-bouazzouni]

The new Algorithm

• Come back the code of NCBO
• Make the main lang variable
• Make the secondary lang variable
• First, see if we find a literal that match the main lang
• If not, then if we find a literal without language tag take the first one or all if the list
• If not, then see if we find a literal that matches the secondary lang
• Else take all the ones in the literals array or the first if not list

Exemple

If we set ["en", "fr"] in main_laguages config variable.
We will except to have in order :

1. Attribute values with "en" language tag and values with no language tags
2. Otherwise we take values with "fr" language.
3. Else take all values in the other languages

[syphax-bouazzouni]

Merged in 56fc95c
Feature branch https://github.com/ontoportal-lirmm/goo/tree/pl/add-mainlang-defaults-refactored