Switch to PostgreSQL for the main db

[eubinecto]

why?

• djongo is quite unstable (for some reason database integrity is not maintained).

[eubinecto]

설치 및 실행에 오류가 있었음

여기서 소개한대로 변경을 하니 이제 제대로 실행됨. (brew services restart postgresql, 그리고 createdb)

• https://velog.io/@kim-macbook/postgresql-error-1

[eubinecto]

setting up db viewer

pgadmin looks like a great choice for postgresql.

• https://www.pgadmin.org/download/pgadmin-4-macos/

[eubinecto]

I meant #160 for the commits above..