Database schema and data changes.

Change: 'value_int' column removed from AdditiveProps table. INT values can be saved into the 'value_str' column. They should even take less space if saved there
instead in a INT data type column.
Change: Updated database schema, scripts and screenshot.
Change: xml2sql.py script now correctly generates 'veg' property INT values in SQL script.
Change: Added 'all' a.k.a. 'neutral' locale. Some key/value pairs may be valid for all locales therfore another locale value was needed. Updated locales values in
Models and in db_app_data.sql script.
Return URL for each JSON item fetched.
Added LocalesModel class to handle Local tbl queries.
Refactoring of locale parameters and criteria.

Locale param 'locale' is not working when passed together with the HTTP request. The parameter is translated from string to INT id that will be used when fetching additives data.
Using constants instead of strings in default criteria.
Locale criteria now works for categories.
Added all API specified criteria parameters.

Each model 'get' call is responsible for checking if the request parameters match a list of accepted values. The base SQL query is then prepared with the criteria
specified.
Added empty results validation.

If no results are returned the API responds with Not Found 404.
Removed unused imports. Syntax changes.