Unix socket for database connection

This is a follow-up of the bug #622, but I cannot reopen it, so I open a new one.

There is a library that allows using an unix socket for connecting to the database, [junixsocket](https://kohlschutter.github.io/junixsocket/). I have used it with keycloak, and you only have to add the dependencies to maven, or [whatever scala uses](https://kohlschutter.github.io/junixsocket/dependency-info.html). Then, the connection URL something like this (in my case with postgresql):

`jdbc:postgresql://localhost/keycloakdb?socketFactory=org.newsclub.net.unix.AFUNIXSocketFactory$FactoryArg&socketFactoryArg=/mnt/postgresql/.s.PGSQL.5432&sslmode=disable`

I would simply add this dependency, it's very easy and faster if the DB and docspell are in the same machine.