Implementation of new data model definitions

[howard-e]

Following the drafting up of a new database schema, this aims to provide new Sequelize models to support that migration.

Note that this introduces breaking changes to how models are referenced on the server, queries and existing import scripts.

NB. This was branched off of entity-tests so certain files may be duplicated here as well as tasks that may have come out of the discussion for that related PR #287.

If your database has not been initialized, run:

if [[ "$OSTYPE" == "darwin"* ]]; then
    createdb # run this if the PostgreSQL installation is freshly installed
    yarn db-init:dev;
else
    sudo -u postgres yarn db-init:dev;
fi;

yarn sequelize db:migrate;

Otherwise, you should be able to safely migrate up with:

yarn sequelize db:migrate