Pin flask version for session_cookie_name

[surfer190]

• Update readme for installing dependencies
• Pin flask version

Running the project from clean slate causes this error:

AttributeError: 'Flask' object has no attribute 'session_cookie_name'

Flask changelog indicates:

The session_cookie_name, send_file_max_age_default, use_x_sendfile, propagate_exceptions, and templates_auto_reload properties on app are removed.