Provide task to create a new sites SQLite database

Summary:
To map sites and databases, we need a repository.

This task creates such a repository as a SQLite3 database through PDO,
with a sites table.

The default path for this database is extracted from the environment.

Test Plan: Unit tests provided

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1571