Migrate from SQLite to Postgres

[layertwo]

SQL Alchemy allows for an easy way to point to a different database source. Currently, we're using SQLite for the database.

Some comments: investigate using the database for more than just storing hosts. Build a better user framework, LDAP (as listed in #48), integrations (already such as Netbox), store device data in the database (?).

Stretch: test out using a separate machine for database hosting. Join this with #64.