[FEATURE] Configured in memory test database, postgres test database and database configurations to be used based on NODE_ENV property

[FEATURE] Added invoice_id and memos fields to ripple_transactions table and migrations

[FEATURE] Unit tests for ripple_transactions table including coverage for new invoice_id and memos fields.

[TASK] Reconfigured in memory db testing
Merge pull request #410 from cdmcnamara/in-memory-db

[FEATURE] Configured in memory test database, postgres test database and...