Finish Mailgun templates

[StephenCathcart]

Description 🤔

"As a user, I want to receive emails on account activity, so that I can keep track of any suspicious activity and keep them for auditing purposes."

All Mailgun templates need to be finalized, these are found under templates in the root of the project. A full list of required templates can be found in the email README:

https://github.com/the-pragmatic-dev/meco-api/blob/master/src/main/java/uk/thepragmaticdev/email/README.md

These will need to be added to the Mailgun service on completion.

Acceptance Criteria 🎉

• Ensure that all code conforms to our coding standards
• Written new unit / integration tests (or updated existing ones) for changes if necessary
• Verified that all unit / integration tests are passing
• Written doc blocks, inline documentation and updated READMEs on all new changes if necessary
• Both Travis CI and SonarCloud are passing

Please read CONTRIBUTING.md for details on our code of conduct.