Issue 113 - email template system

[ctlchan]

This pull request introduces an EmailTemplateManager class and a standard for defining future email templates.

Methods

• create(): an asynchronous factory method that registers partials before returning a new instance.
• renderTemplate(): renders a template by a given name followed by the defined standard/convention (see below), returning strings containing a subject line as well as the HTML and plaintext versions of the template.
• previewTemplate(): returns a string for the email preview text.
• getTemplateList(): returns a list of the valid template names that can be passed to renderTemplate() and previewTemplate()

Additional Notes

• both renderTemplate() and previewTemplate()are made generic over EmailTemplateDataMap so that a superset of required parameters to the template are enforced.
• the templates implemented so far are skeleton templates with no styling. Feel free to improve this.
• the EmailService class was modified with a factory method to accommodate the integration of EmailTemplateManager. Changes were made accordingly to authRoutes.ts

Template Definition Convention

• directory names under backend/src/email/templates are used as the template name in Handlebars
• .hbs files with just the template name represent the HTML version of the email
• _subject.hbs, _plain.hbs, and _preview.hbs suffixes after the template name correspond to the subject, plaintext, and email preview respectively (ex. welcome_plain.hbs)

Templates introduced

• welcome
• meetingConfirmation
• update
• passwordReset

[Flapjacck]

LGTM