Adds database configuration and migrations

[jeffmaher]

Note: Do not merge until PR #2 is merged

This PR adds a few things:

• PostgreSQL driver dependency.
• Database configuration/context.
• Utility script for generating a SQL script for the migrations. This can be used for docker-compose and for a real prod migration, otherwise dotnet ef ... commands can be used.
• A test to see if the SQL script for migrations is out of date (i.e. a developer added a migration, but didn't re-generate the script). This can be used after we connect a CI task runner to PRs.
• Updates the docker-compose settings for database stuff (port is exposed externally for dev, removes unused volumes, removes boiler plate blog... text)

It doesn't do these things:

• Provide a sample set of data
• Use the database anywhere in the code

[jeffmaher]

@spartacusmark : Yep -- it supports that! Will add a GUID field.

[jeffmaher]

@spartacusmark and @dsamojlenko : GUID field added into a new migration. Ready for re-review.