Add shell scripts to support Jenkins test jobs and for command line use

* db-drop.sh -- Drops the `ominiwallet` database if it exists, complete without error if it doesn't
* db-init.sh -- Runs two SQL scripts (schema and initialize_data) on `omniwallet`
* db-console.sh -- Opens up a console connection to the `omniwallet` DB

`PGPASSWORD` environment variable can be set to avoid password prompts.