Postgres backend for production/test environments

[stevelaskaridis]

Description

Move from SQLite to PosgreSQL database backend.

Github issues

Closes issues #67 (solved) and #56 (unsolved).

[stevelaskaridis]

Test fails because database configuration is generated from ansible.

[NicolasLiampotis]

The idea is to use SQLite in development and PostgreSQL in staging/production environment. Also SQLite may be used even in production for supporting offline signing (importing/exporting from/to SQLite db files).

So please adjust this PR so that both DB backends can be supported as described above. Unless you want to wait for the PR fix for #56 before changing ansible files.

[stevelaskaridis]

The idea is to use SQLite in development and PostgreSQL in staging/production environment.
All right. Will change that.

Also SQLite may be used even in production for supporting offline signing (importing/exporting from/to SQLite db files).
This is ad-hoc and not really related to the applications main database.

[NicolasLiampotis]

test this please (just to check that Jenkins configuration for pull request builds works)

[NicolasLiampotis]

retest this please (Jenkins configuration for pull request builds should actually work this time)