Added sqlalchemy to the project

[ZapAnton]

TODO:

- Share sqlalchemy engine between modules in projects (to be able to call sqlalchemy functions from different modules)

• Add standard styles when db is initialized
• Replace show_all_styles function with the sqlalchemy function
• Replace chosen_style_exists function with the sqlalchemy function
• Replace get_style_by_name function with the sqlalchemy function
• Implement formatting for the style body from the db (replace the {@} sign with the user input).

[abitrolly]

Better use combined DATABASE_URL and make it possible to override from os.environ (https://12factor.net/backing-services).