Usability improvements for Pongo shell

[oskardudycz]

Added:

• PostgreSQL connection check,
• an option to set the prettifying and log level through shell params and helper methods,
• direct access to collections in shell,
• an option to disable auto-migrations,
• option to directly call sql from db,
• printing migration sql based on the config file

Fixed:

• returning information about not-successful operations,
• shell handling,