Send email notifications

[chidimo]

What does this PR do?

Send out email notifications

Description of Task to be completed?

1. Send email notifications on signup, loan application, and rejection or approval of a loan
2. Improve test coverage and maintainability

How should this be manually tested?

1. Clone the repo
2. cd into the root folder on a cmd shell and run yarn install. PowerShell is fine also.
3. Setup a PostgreSQL DB.
4. Define a .env file in the root of the project and supply values for the following parameters

   JWT_SECRET=<json-web-token-secret>
   DBNAME=<database-name>
   PGPASSWORD=<postgres-db-password>
   PGHOST=<postgres-db-host>
   PGUSER=<postgres-db-user>
   PGPORT=<postgres-db-port>

5. Create a PostgreSQL database called testdb.
6. Run command yarn test

Any background context you want to provide?

What are the relevant pivotal tracker stories?

165839924
166182329
166135690

Screenshots (if appropriate)

Nil

Questions:

Nil