BO44 - create DAL utilities to store localized fields

[gregoriopalama]

Create DAL utilities to store localized fields in Firestore.
The field should become a map, with the locale as index and the localized string as the value.

• The utilities will have access to the language actually configured as default
• The utilities will have access to the actual language used by the FrontEnd
• The utilities will merge the incoming changes to the values that are already on the DB, if present
• After the merge, the utilities will check if all the LocalizedString fields have a value for the default language. If this is not the case, then an error must be fired