Allow local changes to db seeds

Before, `$ rake db:seed` recreated the database according to out-of-date schema.sql and seeds.sql files fetched from the internet.

This overwrote local database schema changes and local changes to seeds.sql.

This pull request adds schema.sql and seeds.sql to version control, allowing local changes. `$ rake db:seed` will now use the local seeds file rather than fetching it from the internet.

Other changes:

Delete seeds.sql sections which referred to db tables that no longer exist

When seeding database, do not drop and recreate the local database - instead
keep the existing local database

Automatically regenerate schema.sql after any local migration to ensure it
matches current database schema