Common services for the REST service

The module includes the following packages:

• db

  PostgreSQL instance, instance creator and custom methods (based on the pgx driver)

• exception

  a set of functions that write JSON encoded errors to http.ResponseWriter

• formdata

  Middleware that saves files and "restore" JSON (requires custom FormData converter on frontend)

• jwt

  Generates and validates JWT (based on jwt-go)

• mail

  Some basic functions to send a mail using net/smtp

• spa

  http.Handler for serving SPA and static files

• uploads

  http.Handler for serving uploads protected by access token.