- feat(examples/database): added models and versions examples;

[CESSIDY]

Added a directory to store examples: /src/python/src/examples/ Added examples of migrations (/src/python/src/examples/database/versions/):

• create_cities_table;
• create_states_table;
• create_countries_table;
• create_first_names_table;
• create_last_names_table;

Added example models (/src/python/src/examples/database/models/):

• cities.py;
• countries.py;
• first_names.py;
• last_names.py;
• states.py;